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The Semantic Web
Teacuteleacutecom ParisTechSummer 2012
by Fabian M Suchanek
This document is available under aCreative Commons Attribution Non-Commercial License
2
Organization
bull Lecture 1330-1500
bull Pause 1500-1515
bull Lecture 1515-1645
bull Web site httpsuchaneknameworkteaching
3
Knowledge RepresentationYou have seen different ways to represent knowledge
bull in PROLOG alive(Elvis) is(Elvis alive)
bull in Neural Networks
bull in natural language
ldquoElvis is aliverdquo
bull in XML ltalivegtElvisltalivegt
bull in first order logic x rocksinger(x) =gt alive(x)
A
bull in a mathematical notation elvis εAlive
bull in a database
bull in propositional logic elvis_alive Perso
nStatus
Elvis alive
Now how does it look in real life
4
MotivationIn reality knowledge is represented in many different ways This makes data interaction difficult
Person
Job
Elvis singer
Person
Occupation
Elvis P singer
ltxmlgt ltpersongt ltoccupationgt singer
5
Motivation
Person
Job
Elvis singer
The interaction is particularly difficult if the data resides on different machines or devices
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
6
Motivation
Person
Job
Elvis singer
and even more difficult if the data format stems from different companies
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
7
Use casesExamplesbull Booking a flight Interaction between office computer flight company travel agency shuttle services hotel my calendar
bull Finding a restaurant Interaction between mobile device map service
recommendation service restaurant reservation service
bull Web search Interaction between client search service
Web page content provider
Use cases
8
bull Intelligent home Fridge knows my calendar orders food if I am planning a dinner
bull Intelligent cars Car knows my schedule where and when to get gas how not to hit other cars what are the legal regulations
bull Web service composition Interaction between client and Web services and
Web services themselves
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
2
Organization
bull Lecture 1330-1500
bull Pause 1500-1515
bull Lecture 1515-1645
bull Web site httpsuchaneknameworkteaching
3
Knowledge RepresentationYou have seen different ways to represent knowledge
bull in PROLOG alive(Elvis) is(Elvis alive)
bull in Neural Networks
bull in natural language
ldquoElvis is aliverdquo
bull in XML ltalivegtElvisltalivegt
bull in first order logic x rocksinger(x) =gt alive(x)
A
bull in a mathematical notation elvis εAlive
bull in a database
bull in propositional logic elvis_alive Perso
nStatus
Elvis alive
Now how does it look in real life
4
MotivationIn reality knowledge is represented in many different ways This makes data interaction difficult
Person
Job
Elvis singer
Person
Occupation
Elvis P singer
ltxmlgt ltpersongt ltoccupationgt singer
5
Motivation
Person
Job
Elvis singer
The interaction is particularly difficult if the data resides on different machines or devices
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
6
Motivation
Person
Job
Elvis singer
and even more difficult if the data format stems from different companies
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
7
Use casesExamplesbull Booking a flight Interaction between office computer flight company travel agency shuttle services hotel my calendar
bull Finding a restaurant Interaction between mobile device map service
recommendation service restaurant reservation service
bull Web search Interaction between client search service
Web page content provider
Use cases
8
bull Intelligent home Fridge knows my calendar orders food if I am planning a dinner
bull Intelligent cars Car knows my schedule where and when to get gas how not to hit other cars what are the legal regulations
bull Web service composition Interaction between client and Web services and
Web services themselves
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
3
Knowledge RepresentationYou have seen different ways to represent knowledge
bull in PROLOG alive(Elvis) is(Elvis alive)
bull in Neural Networks
bull in natural language
ldquoElvis is aliverdquo
bull in XML ltalivegtElvisltalivegt
bull in first order logic x rocksinger(x) =gt alive(x)
A
bull in a mathematical notation elvis εAlive
bull in a database
bull in propositional logic elvis_alive Perso
nStatus
Elvis alive
Now how does it look in real life
4
MotivationIn reality knowledge is represented in many different ways This makes data interaction difficult
Person
Job
Elvis singer
Person
Occupation
Elvis P singer
ltxmlgt ltpersongt ltoccupationgt singer
5
Motivation
Person
Job
Elvis singer
The interaction is particularly difficult if the data resides on different machines or devices
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
6
Motivation
Person
Job
Elvis singer
and even more difficult if the data format stems from different companies
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
7
Use casesExamplesbull Booking a flight Interaction between office computer flight company travel agency shuttle services hotel my calendar
bull Finding a restaurant Interaction between mobile device map service
recommendation service restaurant reservation service
bull Web search Interaction between client search service
Web page content provider
Use cases
8
bull Intelligent home Fridge knows my calendar orders food if I am planning a dinner
bull Intelligent cars Car knows my schedule where and when to get gas how not to hit other cars what are the legal regulations
bull Web service composition Interaction between client and Web services and
Web services themselves
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
4
MotivationIn reality knowledge is represented in many different ways This makes data interaction difficult
Person
Job
Elvis singer
Person
Occupation
Elvis P singer
ltxmlgt ltpersongt ltoccupationgt singer
5
Motivation
Person
Job
Elvis singer
The interaction is particularly difficult if the data resides on different machines or devices
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
6
Motivation
Person
Job
Elvis singer
and even more difficult if the data format stems from different companies
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
7
Use casesExamplesbull Booking a flight Interaction between office computer flight company travel agency shuttle services hotel my calendar
bull Finding a restaurant Interaction between mobile device map service
recommendation service restaurant reservation service
bull Web search Interaction between client search service
Web page content provider
Use cases
8
bull Intelligent home Fridge knows my calendar orders food if I am planning a dinner
bull Intelligent cars Car knows my schedule where and when to get gas how not to hit other cars what are the legal regulations
bull Web service composition Interaction between client and Web services and
Web services themselves
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
5
Motivation
Person
Job
Elvis singer
The interaction is particularly difficult if the data resides on different machines or devices
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
6
Motivation
Person
Job
Elvis singer
and even more difficult if the data format stems from different companies
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
7
Use casesExamplesbull Booking a flight Interaction between office computer flight company travel agency shuttle services hotel my calendar
bull Finding a restaurant Interaction between mobile device map service
recommendation service restaurant reservation service
bull Web search Interaction between client search service
Web page content provider
Use cases
8
bull Intelligent home Fridge knows my calendar orders food if I am planning a dinner
bull Intelligent cars Car knows my schedule where and when to get gas how not to hit other cars what are the legal regulations
bull Web service composition Interaction between client and Web services and
Web services themselves
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
6
Motivation
Person
Job
Elvis singer
and even more difficult if the data format stems from different companies
ltxmlgt ltpersongt ltoccupationgt singer
Person
Occupation
Elvis P singer
7
Use casesExamplesbull Booking a flight Interaction between office computer flight company travel agency shuttle services hotel my calendar
bull Finding a restaurant Interaction between mobile device map service
recommendation service restaurant reservation service
bull Web search Interaction between client search service
Web page content provider
Use cases
8
bull Intelligent home Fridge knows my calendar orders food if I am planning a dinner
bull Intelligent cars Car knows my schedule where and when to get gas how not to hit other cars what are the legal regulations
bull Web service composition Interaction between client and Web services and
Web services themselves
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
7
Use casesExamplesbull Booking a flight Interaction between office computer flight company travel agency shuttle services hotel my calendar
bull Finding a restaurant Interaction between mobile device map service
recommendation service restaurant reservation service
bull Web search Interaction between client search service
Web page content provider
Use cases
8
bull Intelligent home Fridge knows my calendar orders food if I am planning a dinner
bull Intelligent cars Car knows my schedule where and when to get gas how not to hit other cars what are the legal regulations
bull Web service composition Interaction between client and Web services and
Web services themselves
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Use cases
8
bull Intelligent home Fridge knows my calendar orders food if I am planning a dinner
bull Intelligent cars Car knows my schedule where and when to get gas how not to hit other cars what are the legal regulations
bull Web service composition Interaction between client and Web services and
Web services themselves
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
9
MergingExamplesbull Adding data to a database From XML files from other databases
bull Merging data after company mergers (eg Apple buys Microsoft) Different terminology has to be bridged accounts to be merged
bull Merging data in research eg biochemical genetic pharmaceutical research data
(Less exciting but probably more frequent)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
10
The Semantic Web
Idea We need an infrastructure that allows computers to ldquounderstandrdquo their data
This infrastructure shallbull allow machines to process data from other machinesbull ensure interoperability between different schemas
devices and organizationsbull allow data to describe databull allow machines to reason on the databull allow machines to answer semantic queries
This is what the Semantic Web aims at
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
11
The Semantic Web
The Semantic Web is an evolving extension of the World Wide Web in which data is made available in one standardized semantic format
hellip we will learn more about this format in a minute
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
12
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data1935
singer
born
Elvis where are you
born
bull Publish data (RDFa)
Ontology
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
13
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
Standards produced byor endorsed by theWord Wide Web Consortium(W3C)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
14
Identifying EntitiesWe want to find words for entities that are understoodglobally
Elvis Presley
The King
Le Roi du Rocher et Tourner
Elvis
very difficult
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
15
Identifying EntitiesEven if we agree for a name for an entitysomeone else may use the name for a different thing
Elvis Presley Elvis Presley
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
16
URIsA URI is a globally unique identifier for an entity
httpelvisorgElvis httpimitatorscomElvis
We can use eg a URL as a URI
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
17
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)
httpelvisorgElvis httpimitatorscomElvis
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
18
URIsA URIs arebull globally unique (the same string is the same identifier)bull unambiguous (the same URI stands for the same thing)bull but possibly synonymous (same thing has multiple URIs)
httpelvisorgElvis httpmusiciansorgPresley
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
19
URIs
httpelvisorgElvis httpmusiciansorgPresley
If two people use different URIs they could be talking about the same thingIf two people use the same URI it is sure that they are talking about the same thing
httpimitatorscomElvis
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
20
URIs and URLs
httpelvisorgme Identifies the person not Internet-accessible
httpelvisorgindexhtml Identifies a fileInternet-accessible
Age
77
5
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
21
NamespaceshttpimitatorsorgElvisFG17
World-wide uniquemapping to domain owner
in the responsibilityof the domain owner
The domain provides a ldquonamespacerdquo ie a range of identifiers that cannot collide with other
identifiers
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
22
Namespaces
httpimitatorsorgElvis
httpelvisorgElvis httpelvisorgPriscilla
httpimitatorsorgMadonna
httpimitatorscom
httpelvisorg
Within his namespace everybody can use the names he wants
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
23
URI Use Cases
People can invent all kinds of URIsbull a company can create URIs to identify its productsbull an organization can assign sub-domains and each sub-domain can define URIsbull individual people can create URIs from their homepagebull people can create URIs from any URL for which they have exclusive rights to create URIs
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
24
URNsA Uniform Resource Name (URN) is a URI that is globally assigned
ldquournrdquo + Namespace + ldquordquo + Identifier
A URN takes the following form
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
25
URN AssignmentStep 1 The IANA (Internet Assigned Numbers Authority)assigns namespaces to specific organizations
Step 2 The organization specifies identifiers for its entities in its namespace
IANA
InternationalStandards Organization
InternationalBankingOrganization
can uselsquoisbnrsquo
can use lsquoswiftrsquo
urnisbn42424242 urnswiftSAN1003
examples arehypothetical
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
26
Syntax of URNs
urnisbn123456789
Example
Identifier assigned by ISO to a book
Namespace assigned by IANA to the International Standards Organization (ISO)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
27
Example URNs
ISBN (Books) urnisbn1234567
ISAN (Journals) urnisan0000-1111-2222-3333-4444
SWIFT (Banks) urnswiftbicBYLADEM1000
examples arehypothetical
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
28
Example URNs OIDs
OID (Object Ids) urnoid216840
Example
Object IDs are identifiers form one global tree of identifiers where sub-trees are administrated by authoritiesFor example the IANA administrates ids for companies
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
29
Example URNs UUIDs
UUID (Universally unique ids) urnuuid6e8bc430-9c3a-11d9-9669-0800200c9a66
A Universally Unique ID (UUID) is a software-generated string that is globally unique
Computed eg by using bull the MAC address (identifier of the computer)bull plus a timestamp
Example run ifconfig getmac
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
30
URIs SummaryA Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
The goal is to give ldquoall things on Earthrdquo a unique identifier
Two main approaches1 URL-like identifiers2 Uniform Resource Names (URNs)
URNs URLs
URIs
Propose another real-world domain where we could establish URNs
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
31
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
32
RDFThe Resource Description Framework (RDF) is a standardizedknowledge representation model that resembles the entity-relationship model
An RDF statement (triple) is a triple of 3 URIs calledthe subject the predicate and the object
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
33
RDF
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
identifies identifies
the relationship of winning something
identifies
Grammy Award
ldquoElvis won the Grammy Awardrdquo
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
34
RDF Graphs
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
Elvis Presley
won
Grammy Award
A set of RDF statements is isomorphic to a labeled directed multi-graph which is the notation we will use here
The subject and object of a triple correspond to nodesthe predicate corresponds to directed edge from subject to object with a label given by the predicate
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
35
Sample RDF Graph Example Elvis in YAGO
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
36
Namespace PrefixesA namespace prefix is an abbreviation for the prefix of a URI
elvishimself inriawon grammyprize
prefix elvis lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
A URI abbreviated this way is called a qname
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
37
Default Prefix
himself inriawon grammyprize
prefix lthttpelvisorggtprefix inria lthttpinriafrrdfdtagtprefix grammy lthttpg-acomgt
httpelvisorghimself httpinriafrrdfdtawon httpg-acomprize
The default namespace prefix is just a colon
In the following we assume such a prefix
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
38
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize
Elvis Grammy Award
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
39
Tabular Data in RDF
GrammyAward
All tabular data can be expressed in RDF
won
Person
Prize Country
Elvis Grammy Award USA
USA
isFrom
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
40
Event EntitiesAll tabular data can be expressed in RDF
Person
Prize Year
Elvis Grammy Award 1967
GrammyAward
1967
Event42 year
prize
person
Event42
Event entities are artificial entities that representa complex constellation
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
41
Exercise
Represent the following information in an RDF graph
Elvis was born in TupeloTupelo is located in MississippiElvis married Priscilla in 1967Priscilla likes Mississippi
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
RDF Semantics
GrammyAwardwon
NatAcademypresents
A triple ltspogt is interpreted as a First Order Logic fact p(so)
won(Elvis GrammyAward)presents(NatAcademy GrammyAward)
42
The triple of URIs ltspogt the graph and the First Order Logic fact are equivalent representations of the same statement
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Notation 3
43
Notation 3 (N3) is a concrete syntax for RDF
prefix lthttpinriafrgt prefix elvis lthttpelvisorggt
NatAcademy presents lthttpg-acomprizegt
elvishimself won lthttpg-acomprizegt plays ltguitargt
Qnames or URIs
Same subject can be abbreviated
GrammyAwardwon
NatAcademypresents
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
RDF XML Syntax
44
RDF can also be stored in XML format
ltxml version=10gtltrdfRDF xmlnsrdf=ldquohttpwwww3orgnsrdquo xmlnsi=ldquohttpinriafrrdfdtardquogt
ltrdfDescription rdfabout=ldquohttpelvisorghimselfrdquogt ltiwon rdfresource=ldquohttpAwardldquo gt ltrdfDescriptiongt
Properties of X are listed inside an rdfDescription about=X
GrammyAwardwon
NatAcademypresents
Namespaces become XML namespaces
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
RDF in a Database
45
RDF can also be stored in a database
Subject Predicate
Object
httpelvisorghimself
won httpg-acomprize
GrammyAwardwon
NatAcademypresents
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
46
Labels
ldquoElvisrdquo ldquoThe Kingrdquo
rdfslabelrdfslabel
A label is a human-readable name for an entity
Synonymy Two labels share the same entity
Ambiguity One label refers
to different entities
Find 1 example for synonymyand 1 example for ambiguity
Another namespacewhich we will see later
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
47
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
48
ClassesA class (also called concept) can be understood as a set of similar entities
person
singer
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
49
Classes in RDF
singer
The fact that an entity belongs to a class is expressed by the type predicate from the standard namespace rdf
rdftype
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
50
Classes in RDF
rdftype
The fact that a class is a sub-class of another class is expressed by thesubclassOf predicate from the standard namespace rdfs
person
rdfssubclassOf
singer
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
51
Taxonomy
singer
rdftype
A taxonomy is a hierarchy of classes
person
Resource
rdfssubclassOf
rdfssubclassOf
unemployed
rdftype
theory
abstraction
rdftype
rdfssubclassOf
taxo
nom
yin
stan
ces
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
52
Taxonomy
singer
rdftype
person
rdfsResource
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
The most general class is rdfsResource ndash everything is a resource
More special class
More general class
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
53
Taxonomy
singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
taxo
nom
yin
stan
ces
X is a class if we can say ldquoI met an Xrdquo
X is a sub-class of Y if we can say ldquoEvery X is a Yrdquo
Everything with a proper name is an instance
Make a taxonomy of animals
Include at least 2 instances
rdfsResource
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
54
RDFS ldquoMeta Factsrdquo
rdfsClass
rdfssubclassOfrdftype
rdftype singer
rdftype
person
rdfssubclassOf
rdfssubclassOf
rdfsResource
rdftype
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
55
PropertiesProperties (predicates) themselves resources
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
won
Singer
rdftype
rdfsubclassOf
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
56
PropertiesIn triple format anyway everything is just triples
won
rdfProperty
rdftype
rdfssubclassOfrdftype
rdfsResource
Elvis won GrammyrdfProperty rdftype rdfsResourcewon rdftype rdfProperty
won
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
57
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
rdfsrangerdfsdomainPerson Prizewon
rdfProperty
rdftype
won
As first argument of won we expect persons
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
58
Domain amp RangeThe domain of a predicate is the class of the instances expected as first argument The range is the class of instances expected as second argument
Write down the domains and rangesof the following predicates
bull graduatedFrom (eg Elvis graduatedFrom ParisTech)bull bornIn (eg Elvis bornIn Tupelo)bull hunts (eg Tom hunts Jerry)bull rdftypebull rdfsubclassOf
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
59
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classes
rdftype
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
60
Semantics of rdftype
singer
rdftype
person
rdfssubclassOf
Every instance is an instance of all more general classesWe express this by a deduction rule
rdftype
X rdftype YY rdfssubclassOf Z
X rdftype Z
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
61
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule is of the form A Bwhere B is a literal and A is a set of literalsA literal is a triple that can contain variables
set of 2 literals A
single literal B
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
62
Deduction Rules
X rdftype YY rdfssubclassOf Z
X rdftype Z
A deduction rule A B meanswhenever there is a set of triples that match Aadd the triple B with the variables instantiated
Elvis rdftype SingerSinger rdfssubclassOf Person
Elvis rdftype Person
match
add
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
63
RDFS Deduction RulesRDFS specifies 44 deduction rules
The rules are applied recursively until the set of triples doesnot change any more
The result is called the deductive closure
A1
B1
A44
B44
s0 p0 o0s1 p1 o1s2 p2 o3s3 p3 o4s4 p4 o4
s5 p5 o5
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
64
SubclassOf Rule
singer
rdftype
person
rdfssubclassOf
rdfssubclassOfX rdfssubclassOf YY rdfssubclassOf Z
X rdfssubclassOf Z
Every class is a subclass of all more general classes
rdfssubclassOfrdfsResource
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
65
Domain amp Range Rules
singer
R rdfsrange CX R Y
Y rdftype C
won
Prize
rdftyperdftype
wonrdfsrangerdfsdomain
R rdfsdomain CX R Y
X rdftype C
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
66
Sub-Properties
won
wonAlone
ltPsubpropertyOfRgtltXPYgt
ltXRYgt
rdfssubpropertyOf
wonAlone
won
A sub-property of a predicate R is a more special variant of R
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
67
P rdfssubpropertyOf RX P YX R Y
R rdfsdomain DX R YX rdftype D
R rdfsrange CX R YY rdftype C
X rdftype YY rdfssubclassOf ZX rdftype Z
X rdfssubclassOf YY rdfssubclassOf ZX rdfssubclassOf Z
wonAlone
won
wonAlone
rdfssubpropertyOf
herordfsdomain
personrdfssubclassOf
Compute the deductive closure
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
68
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
69
Storing dataRDF data is usually stored on a server
gGrammy Award
gPrize
rdftype
gNatAcademy
gpresents
Namespaceg = httpg-acom
prefix g httpg-acom prefix rdf httpwwww3org
gGrammyAward rdftype gAward
gNatAcademy gpresents gGrammyAward
The server at httpg-acom stores
Try this
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
70
Storing data
The ontology is shown here in the graphical form but it is stored on the server in textual form
Example The YAGO ontology is stored at the server at httpyago-knowledgeorg
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
71
URIs
A URI is not necessarily dereferenceable (ie it cannot be accessed online)
httpg-acomGrammyAward =gt NOT FOUND
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
72
Cool URIs
But URIs can be dereferenceable This means that if I access the URL the server responds with an RDF snippet
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Try this out rdftype = httpwwww3org19990222-rdf-syntax-nstype
httpg-acomGrammyAward click
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
73
URIs can be followed
prefix g httpg-acom prefix rdf httpwwww3org19990222-rdf-syntax-ns
gGrammyAward rdftype gAwardhttpelviscomelvis gwon gGrammyAward
Server at httpg-acom replied
The RDF graph becomes traversable
prefix e httpelviscom prefix rdf httpwwww3org19990222-rdf-syntax-ns
eelvis rdftype esingereelvis eborn 1935
Server at httpelviscom replies
click
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
74
Wersquore all one Graph
If two RDF graphs share one node they are actually 1 graph
gGrammy Award 1935
esinger
born
gPrize
ewon
rdftype
Namespacee = httpexampleorg
Namespaceg = httpg-acom
A machine can follow the URIs and retrieve more information in neighboring ontologies
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
75
Shared VocabularyOntologies can share the same nodes
httpelviscomelvis
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
76
Shared VocabularyOntologies can share the same predicates
httpelviscomwon
httpelviscomwon
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
77
Shared VocabularyOntologies can share the same nodes and predicates
Sharing nodes = sharing a vocabulary talking the same language
This has several advantagesbull Reuse of data (modeling work is done only once)bull Higher interoperability (systems use the same vocabulary)bull Distribution of responsibilities (domains modeled by experts)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
78
Standard VocabularyA number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
dc Dublin Core (predicates for describing documents) httppurlorgdcelements11
s Schemaorg (predicates for Web content) httpschemaorg
cc Creative Commons (types of licences) httpcreativecommonsorgns
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
79
Standard Vocabulary
Standard vocabulary provided by the W3Cbull type bull subclassOf bull Property bull Classbull labelbull hellip
A number of standard vocabularies have evolved
rdf The basic RDF vocabulary httpwwww3org19990222-rdf-syntax-ns
rdfs RDF Schema vocabulary httpwwww3org19990222-rdf-syntax-ns
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
80
Dublin Coredc Dublin Core (predicates for describing documents) httppurlorgdcelements11
httpelvisorgbiohtml ldquoA biography of Elvisrdquo
dcTitleFabiandcCreator
ldquoThis is the entire life ofrdquo
dcDescriptionldquoTextrdquo
dcType
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
81
Creative Commonscc Creative Commons (types of licences) httpcreativecommonsorgns
ccBYcclicense
httpfabianorg
ccAttributionUrl
ccReproductionldquoFabianrdquoccAttributionName
ccWork
ccpermitsrdftype
Try this
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
82
Schemaorgs schemaorg (vocabulary for things on the Web) An alliance of Microsoft Google and Yahoo () httpschemaorg
sPriscillasspouse
ldquoElvis Presleyrdquosname
sPerson
Schemaorg defines vocabulary for people movies events restaurants etc
Similar Googlersquos data vocabulary Facebookrsquos open graph
Try it out
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
83
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
84
The Goal of OWLRDFS just allows us to define classes and subclasses with very limited inference
Can we go further
bull Reasoning If X is left of Y and Y is left of Z then X is left of Zbull Class definitions The class of husbands is the class of married menbull Class properties People and tables are two disjoint classes
Goal of the Web Ontology Language(OWL)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
85
OWL VocabularyOWL is a namespace that defines predicates with certain semantic rules
Man
Father
Parent
listowlIntersectionOf
rdftypeX rdftype CC owlintersectionOf LISTLIST hasElement Z
X rdftype Z
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
86
OWL UndecidabilityOWL defines so powerful predicates that it is undecidable
owloneOf
owltwoOf
owlreflexiveIntersectionOf
owlcomplicatedCombinationOf
owlhyperSymmetricProperty
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
The ldquolistrdquo is an RDF list with predicates defined there
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
87
OWL-DL GoalOWL-DL is a subset of OWL that is decidable
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
owlinverseowlcardinality
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
88
OWL-DL Notation
Man
Father
Parent
listowlIntersectionOf
rdftype
hasElementhasElement
father = parent | | man
This notation is equivalent to the RDF graph representation
OWL-DL comes with a simplified notation called Description Logic
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Intersection
89
X | | Y = the class of things that are in both X and Y
father = parent | | malePerson
If X and Y are classes then we define
Example
The class of fathers is the intersection of the classes parent and malePerson
OWL-DL is primarily concerned with describing sets of entities fathers mothers birds universities
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Intersection
90
father = parent | | malePerson
malePerson parentfa
ther
Class intersection has a set-theoretic interpretation
Class intersection also has a first order logic interpretation
x father(x) lt= gt parent(x) malePerson(x)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Union
91
X | | Y
person = man | | woman
= the class of things that are in X or in Y
If X and Y are classes then we define
Class union also has a set-theoretic interpretation
woman man
person
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Union Intersection Negation
92
X | | YX | | Y~X
= (parent | | man) | | (hardRockSinger | | softRockSinger) | | ~married
= person | | ~(hardRockSinger | | softRockSinger)
person parent hardRockSinger softRockSinger happyPerson marriedPerson malePerson
unmarried-rock-singing-father
non-rock-singing-person
rockSinger = hardRockSinger| | softRockSinger
The class of things that are in X or in YThe class of things that are in both X and YThe class of things that are not in X
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
93
RestrictionsRC The class of things where there is at least one R-link to an instance of C
E
R A predicateroleC a class
has-happy-child = hasChildhappyPerson
E
This corresponds to the First Order Logic formula x has-happy-child(x) lt=gt y hasChild(xy) happyPerson(y)
hasChildhappyPerson
hasChild
hasHappyChild
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
94
RestrictionsRC The class of things where all R-links lead to a C
A
has-only-happy-children =
hasChildhappyPerson
A
This corresponds to the First Order Logic formula x has-only-happy-children(x) lt=gt y hasChild(xy) =gt happyPerson(y)
hasChild
hasChild
happyPerson
hasHappyChild
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
95
RestrictionsRC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
singer-with-happy-child =
singer | | hasChildhappyPerson
singer-with-only-happy-children =
singer | | hasChildhappyPerson
A
E
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
96
Subclass Assertions
X | Y X is a subclass of Y (everything in X is also in Y)
happysingers| singer | | hasChildhappyPerson
singer | person
This corresponds to the First Order Logic formula x singer(x) =gt person(x)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
97
Exercise
RC The class of things where all R-links lead to a CRC The class of things where there is a R-link to a C
EA
X | | YX | | Y~X
The class of things that are in both X and YThe class of things that are in X or in YThe class of things that are not in X
X | Y X is a subclass of Y (everything in X is also in Y)
Assume the classes male person happyPerson and the predicates marriedTo hasChild
bull build the class of married peoplebull build the class of people married to at least 1 happy persbull build the class of happy male married peoplebull say that married people are happy
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
98
Type Assertionsa C a is of type C (a is in C)
elvis singer | | hasChildhappyPerson
elvis singer
This corresponds to the First Order Logic formula
singer(elvis)
The set-theoretic interpretation is ldquois an element ofrdquo
happyPerson
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
99
Fact Assertions(XY) R X and Y stand in relationship R
(elvislisa) hasChild
This corresponds to hasChild(elvislisa)
(elvispriscilla) marriedTo
This corresponds to marriedTo(elvispriscilla)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
100
OWL-DLOWL-DL basically reasons about properties such as
bull having a link to an element of a class
ldquoThose that have a female childrdquo
EhasChildfemale
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
101
OWL-DL
bull having all links of one type leading to a certain class
ldquoThose thathave only femalechildrenrdquo
AhasChildfemale
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
102
OWL-DL
bull being in two classes at the same time
ldquoThose thathave a child and have only femalechildrenrdquo
hasChildperson AhasChildfemale
X | |Y
bull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
E
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
103
OWL-DL
elvis hasChildfemale
AhasChildfemale
Abull being in two classes at the same timebull having all links of one type leading to a certain class
OWL-DL basically reasons about properties such as
bull having a link to an element of a class
bull belonging to such a class
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
104
OWL-DL
bull standing in a relationship
(elvis pricilla) marriedTo
marriedTo
bull being in two classes at the same timebull having all links of one type leading to a certain class bull having a link to an element of a class
bull belonging to such a class
OWL-DL basically reasons about properties such as
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
105
OWL-DLOWL-DL infer properties to make the knowledge baseconsistent
Whatever other children Priscilla has will become girls
AhasChildfemale
(priscilla navarone)hasChildpriscilla hasChildfemale
=gt navaronefemale
This may fail of course
navaronemalemale | | female |
T
Empty class
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
106
Reasoning TasksClassical reasoning tasks in OWL-DLbull Is the knowledge base consistent
singer | person
bellosingerbellodog
dog| ~person
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
107
Reasoning Tasks
bull Is one class a subclass of another class
hasChildfemale| singer
E
(Are all parents of girls singers)
can be reduced to the consistency problem
(bobLisa) hasChildLisa femalebob~singer
More precisely we ask Does it follow necessarily from the KB that one class is a subclass of the otherIf so we get a contradiction here
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
108
Reasoning Tasks
bull Is an individual an instance of a class
elvissinger can be reduced to the consistency problem
elvis~singer
More precisely we ask Does it follow necessarily from the KB that Elvis is a singer If so this assertion will cause a contradiction
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
109
OWL OWL-DL
bull Does an individual have a certain property
elvis singsgoodSongE
can be reduced to the consistency problemelvis ~ singsgoodSong
E
More precisely we ask Does it follow necessarily from the KB that Elvis sings at least one good song If so this assertion will cause a contradiction
bull Is an individual an instance of a class
bull Is one class a subclass of another class
Classical reasoning tasks in OWL-DLbull Is the knowledge base consistent
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
110
OWL-DL SummaryOWL-DL is a decidable subset of OWL
It is based on the description logic SHOIN(D) a formalism that allows describing properties of objectsin a manner inspired by set theory
A
hasChildfemale
There are a number of free OWL DL reasonersavailable onlinebull Pelletbull FaCT++bull Prova
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
111
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
112
SPARQLSPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
SELECT locWHERE lthttpelvisorgelvisgt lthttpelvisorglivesIngt loc
Find me all the values for loc such that the triple is true
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
113
SPARQL Syntax
SELECT variable variable WHERE literal literal
Note the dot
No comma between variables
variable a name with preceding question mark x y z these are variables
literal an RDF triple that can contain variables Elvis livesIn x
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
114
SPARQL Prefix
SELECT variable variable WHERE literal literal
PREFIX name lturigt
note the colon and the lt gt
SPARQL queries can define and use namespace prefixes
PREFIX e lthttpelvisorggtSELECT locWHERE eElvis elivesIn loc
Example
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
115
SPARQL AnswersAn answer to a SPARQL query on an ontology is an instantiation of the variables so that the query triplesappear in the ontology
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo Priscilla
Answer
loc = Memphis
loc = Memphis
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
116
SPARQL Answers
PREFIX lthttpelvisorggtSELECT locWHERE Elvis livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaElvis livesIn moon
Answer 1
loc = Memphis
loc = Memphis
A SPARQL query can have multiple answers
Answer 2
loc = moon
loc = moon
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
117
SPARQL Answers
PREFIX lthttpelvisorggtSELECT x locWHERE x livesIn loc
Query
Ontology
Elvis livesIn MemphisElvis marriedTo PriscillaPriscilla livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
Answer 2x = Priscillaloc = moon
x = Priscillaloc = moon
A SPARQL query can have multiple variables
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
118
SPARQL Answers
PREFIX SELECT xWHERE x livesIn Memphis x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerPriscilla livesIn MemphisPriscilla rdftype Actress
Answer
x = Elvis
x = Elvis
A SPARQL query can have multiple triples
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
119
SPARQL Answers
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = Memphis
A SPARQL query with multiple triples variables and answers
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
120
SPARQL Answers
Query
Ontology
Elvis livesIn MemphisElvis rdftype SingerElvis livesIn moon
Answer 1
x = Elvisloc = Memphis
x = Elvisloc = moon
A SPARQL query with multiple triples variables and answers
Answer 2
x = Elvisloc = moon
PREFIX SELECT x locWHERE x livesIn loc x rdftype Singer
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
121
SPARQL MatchingAnswering SPARQL queries can be seen as matching sub-graphs
Elvis where are you
elivesInmoon
PREFIX e lthttpelvisorggt
SELECT locWHERE eelvis elivesIn loc
elivesIn loc
loc = emoon
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
122
SPARQL EndpointsMany ontologies provide a ldquoSPARQL endpointrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
httpwwww3orgwikiSparqlEndpoints
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
123
SPARQL Example
select distinct x lthttpdbpediaorgresourceElvis_Presleygt lthttpwwww3org19990222-rdf-syntax-nstypegt xlimit 100
Example at httpdbpedia-liveopenlinkswcomsparql
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
124
SPARQL SummarySPARQL (SPARQL Protocol and RDF Query Language) is the query language of the Semantic Web
PREFIX e lthttpelvisorggt SELECT xWHERE x ewon eGrammy
SPARQL borrows concepts from SQL but is specially adapted to distributed RDF graphs
Many ontologies provide ldquoSPARQL endpointsrdquo ie a service than canbull receive SPARQL queries sent by a machinebull receive SPARQL queries typed by a human in a Web interface
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
125
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFa)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
126
Linked Data Problem
singerMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
rdftype
Ontologies can talk about the same thing with different URIs
httpeporgElvis
httpmporgTheKing
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
127
Linked Data Problem
guitarMusiPedia(httpmporg )
rdftypeElvisopedia(httpeporg )
singer
plays
Ontologies can contain complementary information aboutthe same entity with different URIs
httpeporgElvis
httpmporgTheKing
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
128
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be used
httpeporgElvis
httpmporgTheKing
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
129
Linked Data Problem
guitar
rdftype
SELECT xWHERE x rdftype singer x plays guitar
singer
plays
Different URIs for the same thing are a problem becausecomplementary information cannot be usedeven if the data is merged
httpeporgElvis
httpmporgTheKing
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
130
Linked Data Solution
guitar
rdftypesinger
plays
httpeporgElvis
httpmporgTheKing
OWL provides vocabulary to link equivalent entitieswith different URIs
owlsameAs
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
131
The Linking Data ProjectThe Linking Open Data Project aims to interlink all open RDF data sources into one gigantic RDF graph (link)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
132
The Linked Data Cloud
Currently (2012) bull 295 ontologiesbull 25 billion triplesbull 400m links httprichardcyganiakde200710lodimagemaphtml
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
133
Existing OntologiesThe existing ontologies in the Linked Data Cloud include ( httpwww4wiwissfu-berlindelodcloud )bull US census databull BBC music databasebull Gene ontologiesbull general knowledge YAGO DBpedia Cyc bull US and UK government databull geographical data in abundancebull national library catalogs (USA Germany etc)bull publications (DBLP)bull commercial productsbull all Pokemonsbull and many more
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
134
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (RDFaMicroformatsMicrodata)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
135
And the rest of the Web
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
136
MicrodataMicrodata is the upcoming W3C standard to annotate HTML pages with RDF data
Similar standards arebull RDFabull Microformats (now becoming obsolete)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
137
Microdata ExampleSuppose we have a page about a researcher
ltdivgt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
138
Microdata
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
Everything inside this ltdivgt becomes a node
httpschemaorgPerson
rdftype
We are using schemaorg vocabulary
The node is of type Person
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
139
Naming a node
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt Martin Thunderbirdltbrgt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
rdftype
We can also give the URI of the node
httpschemaorgPerson
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
140
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemprop=ldquonamerdquogtMartin Thunderbirdltspangt Researcher in RockrsquoNrsquoRoll Music of 1935-1977ltbrgt 3764 Presley Boulevardltbrgt Memphis Tennesseeltdivgt
httpmartin
hellipPerson
rdftype
ldquoMartin Thunderbirdrdquo
name
Statements are constructed with ldquoitemprop=ldquo
Text becomes a string node in RDF
Problem The W3C has not yet agreed on the URI prefix
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
141
RDFa Statements
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt lta itemprop=ldquoworksForrdquo href=ldquohttprrrcomrdquogt Rockrsquon Roll Reseach Institute ltagtltdivgt
httpmartin
hellipPerson
rdftype
httprrrcom worksFor
If the tag contains a ldquohrefrdquo the href target becomes the object
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
142
Inner Nodes
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt
ltspangt ltdivgt
httpmartin
hellipPerson
rdftype
address
itemscope makes a new node
itemprop relates the outer node to the inner node
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
143
Inner Nodes
httpmartin
hellipPerson
rdftype
address
ldquoFrancerdquo
addressCountry
ltdiv itemscope itemtype=ldquohttpschemaorgPersonrdquo itemid=ldquohttpmartin-thunderbirdcommerdquogt ltspan itemscope itemprop=addressrdquogt ltspan itemprop=ldquoaddressCountryrdquogtFranceltspangt ltspangt ltdivgt
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
144
Microdata Vocabulary
lttag itemscopegt defines a new nodelttag itemscope itemtype=urigt defines a new node with rdftypelttag itemscope itemid=urigt defines a new node with URIlttag itemprop=predicategtvaluelttaggt defines a link of the outer node to a literallttag itemprop=predicate href=urlgt defines a link of the outer node to a URI
which is isomorphic to an RDF graph
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
145
Microdata SummaryMicrodata is the upcoming W3C standard to annotate HTML 5 pages with RDF data
bull Grass root appeal(everybody can start annotating pages)
bull No data duplication(all data in one file)
bull Publisher independence (everybody can use his own attributes)
Advantages
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
146
Semantic Web in Action 1
With the Linter parser
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
RDF data following the Open Graph Protocol is often embedded in HTML pagesthus allowing the Facebook LIKE button to work
Semantic Web in Action 2
147
bdquoOpen Graph Protocolldquo httpogporgns
Beautiful mind IMDb
ogpsiteName
ogpMovie
Facebook has developed its own vocabulary the
ogptype
wwwimdbcomtitlett0268978 lthtml xmlnsog=httpogpmens gt hellip ltmeta property=ogtype content=movie gt ltmeta property=fbapp_id content=lsquo123 gt helliplthtmlgt
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Semantic Web in Action 3
148
The major search engines (Google Bing Yahoo) understand (or will understand) RDF data embedded in HTML pages
Try it out
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Semantic Web in Action 4
149
The UK government makes much of its data available online in RDF ndash by law
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Semantic Web in Action 5
150
The DBpedia Mobile App retrieves data from the Linked Open Data Cloud to show places of interest around you
Try it out
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
Semantic Web in Action 6
151
Google launched its ldquoKnowledge Graphrdquo an ontology from Wikipedia that enhances search results
Try it out
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
152
SigmaSigma is a Semantic Web search engine developed at the DERI Ireland It scrapes Embedded RDF and follows owlsameAs (httpsigma)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
153
SigmaSigma also allows the user to correct factually wrong information (such as the urban legend that Elvis would be dead)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
154
The Semantic WebThe Semantic Web provides standards tobull Identify entities (URIs)bull Express facts (RDF)bull Express concepts (RDFS)
bull Describe constraints (OWL)
bull Share vocabularies
bull Query knowledge (SPARQL)
bull Link data
bull Publish data (Embedded RDF)
