Summer School LD4SC 2015 - RDF(S) and SPARQL

LD4SC Summer School7th - 12th June, Cercedilla, Spain


1st Summer School on Smart Cities and Linked Open Data (LD4SC-15)

RDF(S) and SPARQL

Pieter Pauwels, Ghent University


The cool and awesome intro movies

https://vimeo.com/36752317https://www.youtube.com/watch?v=4x_xzT5eF5Q

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https://vimeo.com/36752317



https://www.youtube.com/watch?v=4x_xzT5eF5Q

https://www.youtube.com/watch?v=4x_xzT5eF5Q


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Index

• RDF graphs: the simple basis• Syntax: talking the talk

– URIs– RDF Statements– Literals– Collections and containers

• Linked (Open) Data Cloud• Adding basic structure : RDFS• Querying: SPARQL

– The basis– The SPARQL endpoint– Some more complex examples

• Concluding Overview


RDF graphs, what are they

RDF graphs are DIRECTED, LABELLED GRAPHS

4

P. Pauwels, D. Van Deursen, R. Verstraeten, J. De Roo, R. De Meyer, R. Van de Walle, J. Van Campenhout. A semantic rule checking environment for building performance checking. Automation in Construction 20(5) 2011, 506-518.

LABELLED

DIRECTED

Triple


RDF graphs, what are they NOT

Hierarchies (cfr. XML)

Relational databases (cfr. MySQL, SQLServer)

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RDF graphs are DIRECTED, LABELLED GRAPHS


A triple

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Triple

SUBJECT OBJECTPREDICATE


Connecting Triples

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SUBJECT OBJECTPREDICATE

OBJECT

PREDICATE

OBJECT

PREDICATE

OBJECTPREDICATE


The result: an RDF graph

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LABELLED

DIRECTED

Triple

That is it: simple directed labelled graphs, always remember


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Index







Talking the RDF language

• RDF stands for Resource Description Framework• RDF is a standard data model for describing web resources

– Note: ‘web resources’ can make statements about anything in the real world: DBPedia, geography, building information, sensors, … anything goes

• RDF is designed to be read and understood by computers• RDF is not designed for being displayed to people• RDF is written in XML• RDF is a W3C Recommendation

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http://www.w3schools.com/webservices/ws_rdf_intro.asp

easily used

usually

-> standardisation

not a file format, not a syntax, not a schema, … => a data model

http://www.w3schools.com/webservices/ws_rdf_intro.asp


The Semantic Web stack

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Tim Berners-Lee. WWW past & future, 2003. http://www.w3.org/2003/Talks/0922-rsoc-tbl/.

http://www.w3.org/2003/Talks/0922-rsoc-tbl/


Syntaxes for serialisation

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Triple

RDF/XML

Turtle (TTL)

Notation-3 (N3)

…


Expressiveness of syntaxes

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http://www.w3.org/DesignIssues/diagrams/n3/venn

We stick to Turtle today



Example TTL file

@prefix b: <http://www.R4SC.net/building#> . @prefix c: <http://www.R4SC.net/city#> .

<http://www.R4SC.net/today#building_1> b:hasRoom <http://www.R4SC.net/today#room_1> ; b:hasName “Our summer school building"; c:partOfCity <http://cities.com/#cercedilla> .

<http://cities.com/#cercedilla> c:closeToCity <http://cities.com/#madrid> ;c:hasName “Cercedilla” .

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Example TTL graph


The same thing in RDF/XML

<?xml version="1.0" encoding="UTF-8"?><rdf:RDF xmlns:b="http://www.R4SC.net/building#" xmlns:c="http://www.R4SC.net/city#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <rdf:Description rdf:about="http://www.R4SC.net/today#building_1"> <c:partOfCity rdf:resource="http://cities.com/#cercedilla"/> <b:hasName>Our summer school building</b:hasName> <b:hasRoom rdf:resource="http://www.R4SC.net/today#room_1"/> </rdf:Description> <rdf:Description rdf:about="http://cities.com/#cercedilla"> <c:hasName>Cercedilla</c:hasName> <c:closeToCity rdf:resource="http://cities.com/#madrid"/> </rdf:Description></rdf:RDF>

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Convert to different syntaxes

Convert to/from syntaxes:

http://rdf-translator.appspot.com/

Or simply build and use your own software tool

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18

Index







Uniform Resource Identifiers

URI

URI

URI

URI

URI

URIURI

URI

URI

URI

URI


What is a URI?

• URI stands for Uniform Resource Identifier• Purpose: Obtain globally unique identifiers, so that information

can be exchanged globally.• Structure:

<http://www.R4SC.net/today#building_1>

• Namespace needed to avoid name conflicts with tags of the same name: other tags with the name “building_1” can be defined with other namespace URIs, and an RDF reader would still be able to tell that they were different properties even though they had the same tag name.

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Namespace Name


Full version of the URIs

<http://www.R4SC.net/today#building_1><http://www.R4SC.net/today#room_1>

<http://www.R4SC.net/building#hasRoom ><http://www.R4SC.net/building#hasName >

<http://www.R4SC.net/city#partOfCity><http://www.R4SC.net/city#closeToCity><http://www.R4SC.net/city#hasName>

<http://cities.com/#cercedilla><http://cities.com/#madrid>

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Example TTL file




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Prefixed URIs

@prefix b: <http://www.R4SC.net/building#> . @prefix c: <http://www.R4SC.net/city#> . @prefix bi: <http://www.R4SC.net/today#> . @prefix ci: < http://cities.com/# > .

bi:building_1bi:room_1

b:hasRoomb:hasName

c:partOfCityc:closeToCityc:hasName

ci:madridci:cercedilla

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TTL file with fully qualified names

<http://www.R4SC.net/today#building_1> <http://www.R4SC.net/building#hasRoom >

<http://www.R4SC.net/today#room_1> ; <http://www.R4SC.net/building#hasName > “Our summer school building"; <http://www.R4SC.net/city#partOfCity > <http://cities.com/#cercedilla> .

<http://cities.com/#cercedilla> <http://www.R4SC.net/city#closeToCity > <http://cities.com/#madrid> ;<http://www.R4SC.net/city#hasName > “Cercedilla” .

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-> prefixes increase readibility


25

Index







Statements

Statement

Statement

Statement

Statement

Statement


Statement follows triple structure

<http://www.R4SC.net/today#building_1><http://www.R4SC.net/city#partOfCity > <http://cities.com/#cercedilla> .

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Triple

<http://www.R4SC.net/

today#building_1>

<http://cities.com/#cercedilla>

<http://www.R4SC.net/city#partOfCity>


Combining statements


<http://www.R4SC.net/today#room_1> ; <http://www.R4SC.net/building#hasName > “Our summer school building"; <http://www.R4SC.net/city#partOfCity > <http://cities.com/#cercedilla> .

<http://cities.com/#cercedilla> <http://www.R4SC.net/city#closeToCity > <http://cities.com/#madrid> ;<http://www.R4SC.net/city#hasName > “Cercedilla” .

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Same subject

AND [next statement]

Same subject

Same subjectAND [next statement]

, Same subject, same predicate


List of all statements


<http://www.R4SC.net/today#room_1> .

<http://www.R4SC.net/today#building_1> <http://www.R4SC.net/building#hasName > “Our summer school building” .

<http://www.R4SC.net/today#building_1> <http://www.R4SC.net/city#partOfCity > <http://cities.com/#cercedilla> .

<http://cities.com/#cercedilla> <http://www.R4SC.net/city#closeToCity > <http://cities.com/#madrid> .

<http://cities.com/#cercedilla> <http://www.R4SC.net/city#hasName > “Cercedilla” .

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Statements

Statement

Statement

Statement

Statement

Statement


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Index







Recap on the URIs

URI

URI

URI

URI

URI

URIURI

URI

URI

URI

URI


Literals in the statements


<http://www.R4SC.net/today#room_1> .

<http://www.R4SC.net/today#building_1> <http://www.R4SC.net/building#hasName > “Our summer school building” .

<http://www.R4SC.net/today#building_1> <http://www.R4SC.net/city#partOfCity > <http://cities.com/#cercedilla> .

<http://cities.com/#cercedilla> <http://www.R4SC.net/city#closeToCity > <http://cities.com/#madrid> .

<http://cities.com/#cercedilla> <http://www.R4SC.net/city#hasName > “Cercedilla” .

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Literal

Literal


Conventional representation / distinction from regular resources

Resource

Resource

Resource

Resource

Literal

Literal


Similar yet distinct

@prefix b: <http://www.R4SC.net/building#> . @prefix c: <http://www.R4SC.net/city#> . @prefix xsd: <http://www.w3.org/2001/XMLSchema>.

<http://www.R4SC.net/today#building_1> b:hasName “Our summer school building” ,

“Our summer school building”@en , “Our summer school building”^^xsd:string

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Untyped

Typed

Literal with language setting Referring to type

within specific namespace


What is available in xsd

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http://www.w3.org/TR/xmlschema-2/

http://www.w3.org/TR/xmlschema-2/


What is available in xsd

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http://www.xml.dvint.com/docs/SchemaDataTypesQR-2.pdf

http://www.xml.dvint.com/docs/SchemaDataTypesQR-2.pdf


If you do not like xsd...

Simply define your own datatypes…

@prefix b: <http://www.R4SC.net/building#> . @prefix c: <http://www.R4SC.net/city#> . @prefix dt: < http://www.R4SC.net/todaysdts#> .

<http://www.R4SC.net/today#building_1> b:hasName “Our summer school building”^^dt:myTypeOfString


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Index







Repeating properties

• I have a property that can have multiple values, now what?– Solution 1: Simply repeat the property of the

resource multiple times. – Solution 2: Use a structured value for a literal– Solution 3: Use an RDF Container (Sequence, Bag,

or Alt) or Collection (RDF List)

http://patterns.dataincubator.org/book/repeated-property.html



Example for solution 1: simply repeating property

@prefix b: <http://www.R4SC.net/building#> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

<http://www.R4SC.net/today#room_1> b:hasPersonInside <http://www.R4SC.net/today#PieterPauwels> ,

<http://www.R4SC.net/today#RaulGarciaCastro> ,<http://www.R4SC.net/today#AsuncionGomezPerez> ,<http://www.R4SC.net/today#MariaPovedaVillalon> ,<http://www.R4SC.net/today#FilipRadulovic> .


Example for solution 2: Use a structured value for a literal


<http://www.R4SC.net/today#room_1> b:hasPeopleInside “IRECOGNIZETHIS:PieterPauwels; IRECOGNIZETHIS:

RaulGarciaCastro; IRECOGNIZETHIS:AsuncionGomezPerez; IRECOGNIZETHIS: MariaPovedaVillalon; IRECOGNIZETHIS: FilipRadulovic”

=> NOT recommended!!


Example for solution 3


<http://www.R4SC.net/today#room_1> b:hasPeopleInside ( <http://www.R4SC.net/today#PieterPauwels>

<http://www.R4SC.net/today#RaulGarciaCastro> <http://www.R4SC.net/today#AsuncionGomezPerez> <http://www.R4SC.net/today#MariaPovedaVillalon> <http://www.R4SC.net/today#FilipRadulovic> )


So, what are our options for solution 3?

• Apart from resources and literals, it is also possible to describe ‘containers’ and ‘collections’

• Containers– Bags– Sequences– Alt

• Collections– Lists

used to describe groups that can ONLY contain the specified members

used to describe an open groups of things (unknown length)


Bags – Seqs – Alts ??

• Bag– Unordered– Resources or literals– Duplicate values are permitted

• Sequence (Seq)– Ordered– Resources or literals– Duplicate values are permitted

• Alternative (Alt)– Unordered– Resources or literals– Alternatives for a single property value (cfr. language alternatives)These are the conventions / they are ‘just’ conventions


List

• List– Ordered– Resources or literals– Duplicate values are permitted– Closed collection – length of list is known

• So, identical to a sequence, except that the collection is closed: only the listed items are in the List, nothing else


Back to our example


<http://www.R4SC.net/today#room_1> b:hasPeopleInside ( <http://www.R4SC.net/today#PieterPauwels>

<http://www.R4SC.net/today#RaulGarciaCastro> <http://www.R4SC.net/today#AsuncionGomezPerez> <http://www.R4SC.net/today#MariaPovedaVillalon> <http://www.R4SC.net/today#FilipRadulovic> )


The downside of solution 3<?xml version="1.0" encoding="UTF-8"?><rdf:RDF xmlns:b="http://www.R4SC.net/building#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <rdf:Description rdf:about="http://www.R4SC.net/today#room_1"> <b:hasPeopleInside rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b1"/> </rdf:Description> <rdf:Description rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b4"> <rdf:first rdf:resource="http://www.R4SC.net/today#MariaPovedaVillalon"/> <rdf:rest rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b5"/> </rdf:Description> <rdf:Description rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b5"> <rdf:first rdf:resource="http://www.R4SC.net/today#FilipRadulovic"/> <rdf:rest rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#nil"/> </rdf:Description> <rdf:Description rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b2"> <rdf:first rdf:resource="http://www.R4SC.net/today#RaulGarciaCastro"/> <rdf:rest rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b3"/> </rdf:Description> <rdf:Description rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b1"> <rdf:first rdf:resource="http://www.R4SC.net/today#PieterPauwels"/> <rdf:rest rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b2"/> </rdf:Description> <rdf:Description rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b3"> <rdf:rest rdf:nodeID="fabfea5436e794e259b04593dadf0c9f8b4"/> <rdf:first rdf:resource="http://www.R4SC.net/today#AsuncionGomezPerez"/> </rdf:Description></rdf:RDF>

Blank nodesElaborate and complex description


Repeating properties

• I have a property that can have multiple values, now what?– Solution 1: Simply repeat the property of the

resource multiple times. Repeating properties is the simplest approach to handling multi-valued relations. The alternatives all have their downsides.

– Solution 2: Use a structured value for a literal– Solution 3: Use an RDF Container (Sequence, Bag,

or Alt) or Collection (RDF List)




Wait a second…

Did you say ‘blank nodes’?


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What are blank nodes?

• Blank nodes are nodes that do not have URIs– No URI -> no semantics really -> unstable and unreliable

• They are usually represented as: _:1, _:city, _:thiscanbeanythingyouwishfor, _:8936fazGUID, …

• This representation is typically generated on-the-fly so that it is unique within the scope in which an RDF graph is opened– When opening this RDF graph the following day, even in the

same scope, entirely different names might be generated– Unstable and unreliable


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So, why do we use these blank nodes?

• Simply because it is hard to give everything an explicit name, this is not always wanted / desirable

• For example:

@prefix b: <http://www.R4SC.net/building#> . @prefix c: <http://www.R4SC.net/city#> . @prefix region: <http://www.R4SC.net/region#> .

<http://www.R4SC.net/today#building_1> b:hasRoom <http://www.R4SC.net/today#room_1> ; b:hasName “Our summer school building"; c:partOfCity <http://cities.com/#cercedilla> ;c:partOfRegion [ region:location “NorthOfMadrid”; region:regiontype “Forest”]

• Likewise, people do not intend to define names for all kinds of groups of things -> hence a lot of blank nodes in descriptions of collections and containers

Blank node


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Index







Data integration now possible

MyBuilding Cities


We already integrated datasets!


Linked Open Data Cloud

• http://lod-cloud.net/

• datasets that have been published in Linked Data format, by contributors to the Linking Open Data community project and other individuals and organisations

• based on metadata collected and curated by contributors to the Data Hub as well as on metadata extracted from a crawl of the Linked Data web conducted in April 2014

• Attribution: Linking Open Data cloud diagram 2014, by Max Schmachtenberg, Christian Bizer, Anja Jentzsch and Richard Cyganiak. http://lod-cloud.net/

http://lod-cloud.net/


http://linkeddata.org/

http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData

http://datahub.io/


lod-cloud.net

http://lod-cloud.net (Last version: 2014-08-30)



History of the LOD

http://lod-cloud.net



LOD as of May 2007


LOD as of March 2009


!!!!Advertisement break!!!!

RDF(S) and SPARQLPieter Pauwels

More to come after the break


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http://ldac-2015.bwk.tue.nl/




Before the break


LOD as of August 2014


Circle sizes and arrow fonts

• Depending on the size of the dataset and the number of triples between datasets, the layout in the LOD cloud schema is different.


Data integration now possible

MyBuilding Cities


Status and statistics

• Cumulative stats:http://stats.lod2.eu/ • State of the LOD cloud 2014: http://linkeddatacatalog.dws.informatik.uni-mannheim.de/state/• State of the LOD cloud 2011: http://lod-cloud.net/state/

http://stats.lod2.eu/


http://linkeddatacatalog.dws.informatik.uni-mannheim.de/state/


http://lod-cloud.net/state/




Triple counts





Stats - Datasets by topical domain


Topic Datasets %Government 183 18.05%

Publications 96 9.47%

Life sciences 83 8.19%

User-generated content 48 4.73%

Cross-domain 41 4.04%

Media 22 2.17%

Geographic 21 2.07%

Social web 520 51.28%

Total 1014


http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=government&tags=LinkedDataCrawl2014

http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=publications&tags=LinkedDataCrawl2014

http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=lifesciences&tags=LinkedDataCrawl2014

http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=usergeneratedcontent&tags=LinkedDataCrawl2014

http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=crossdomain&tags=LinkedDataCrawl2014

http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=media&tags=LinkedDataCrawl2014

http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=geographic&tags=LinkedDataCrawl2014

http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=social+web&tags=LinkedDataCrawl2014

http://linkeddatacatalog.dws.informatik.uni-mannheim.de/dataset?tags=LinkedDataCrawl2014


Stats - Categorization by number of linked datasets

Number of linked datasets Number of datasetsmore than 10 79 (7.79%)

6 to 10 81 (7.99%)

5 31 (3.06%)

4 42 (4.14%)

3 54 (5.33%)

2 106 (10.45%)

1 176 (17.36%)

0 445 (43.89%)




Can my dataset be included?

First, make sure that you publish data according to the Linked Data principles. We interpret this as:• There must be resolvable http:// (or https://) URIs.• They must resolve, with or without content negotiation, to RDF

data in one of the popular RDF formats (RDFa, RDF/XML, Turtle, N-Triples).

• The dataset must contain at least 1000 triples.• The dataset must be connected via RDF links to a dataset that is

already in the diagram. This means, either your dataset must use URIs from the other dataset, or vice versam. We arbitrarily require at least 50 links.

• Access of the entire dataset must be possible via RDF crawling, via an RDF dump, or via a SPARQL endpoint.

Then, add it to the Data Hub and request to be included

http://www.w3.org/DesignIssues/LinkedData.html

http://datahub.io/

http://datahub.io/


The resolvable URIs

Hold on, what do you mean, ‘resolvable’?


Reminder: What is a URI?

• URI stands for Unique Resource Identifier• Purpose: Obtain globally unique identifiers, so that information

can be exchanged globally.• Structure:

<http://www.R4SC.net/today#building_1>

• Namespace needed to avoid name conflicts with tags of the same name: other tags with the name “building_1" can be defined with other namespace URIs, and an RDF reader would still be able to tell that they were different properties even though they had the same tag name.

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Namespace Name


74

What do you mean… resolvable?

• A resolvable URI is: “A URI whose resource has one or more representations available via invoking HTTP GET on the URI”(source: http://www.w3.org/TR/2010/WD-sparql11-http-rdf-update-20100126/)

http://www.w3.org/TR/cooluris/#oldweb

http://www.w3.org/TR/2010/WD-sparql11-http-rdf-update-20100126/

http://www.w3.org/TR/2010/WD-sparql11-http-rdf-update-20100126/




Dereferencing URIs

http://wifo5-03.informatik.uni-mannheim.de/bizer/pub/LinkedDataTutorial/




So, you are now ready to publish here


Note: the O in LOD

• This does NOT mean that RDF is “OPEN” by default

• Most datasets in the LOD cloud have licence information attached

• This does NOT mean that RDF is “OPEN” by default


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Index







What did we do so far?




79



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The RDF namespace

@prefix rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns#


The first few lines


We have actually already used it

<?xml version="1.0" encoding="UTF-8"?><rdf:RDF xmlns:b="http://www.R4SC.net/building#" xmlns:c="http://www.R4SC.net/city#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <rdf:Description rdf:about="http://www.R4SC.net/today#building_1"> <c:partOfCity rdf:resource="http://cities.com/#cercedilla"/> <b:hasName>Our summer school building</b:hasName> <b:hasRoom rdf:resource="http://www.R4SC.net/today#room_1"/> </rdf:Description> <rdf:Description rdf:about="http://cities.com/#cercedilla"> <c:hasName>Cercedilla</c:hasName> <c:closeToCity rdf:resource="http://cities.com/#madrid"/> </rdf:Description></rdf:RDF>

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Need for structured vocabularies

• RDF graphs -> could be anything• Need for semantics / structured vocabularies

Þ RDFSchema (RDFS) Þ Web Ontology Language (OWL)



85




The RDFS namespace

@prefix rdfs: http://www.w3.org/2000/01/rdf-schema#



Example TTL graph

-> ambiguous / close to meaningless


Example vocabulary in TTL

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix b: <http://www.R4SC.net/building#> . @prefix c: <http://www.R4SC.net/city#> .

b:InfrastructuralElementrdf:type rdfs:Class .

b:Buildingrdf:type rdfs:Class ;rdfs:subClassOf b:InfrastructuralElement .

b:hasRoomrdf:type rdf:Property ;rdfs:range b:Room ;rdfs:domain b:Building .

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The same thing in RDF/XML

<?xml version="1.0" encoding="utf-8"?><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"> <rdf:Property rdf:about="http://www.R4SC.net/building#hasRoom"> <rdfs:domain rdf:resource="http://www.R4SC.net/building#Building"/> <rdfs:range rdf:resource="http://www.R4SC.net/building#Room"/> </rdf:Property> <rdfs:Class rdf:about="http://www.R4SC.net/building#InfrastructuralElement"/> <rdfs:Class rdf:about="http://www.R4SC.net/building#Building"> <rdfs:subClassOf rdf:resource="http://www.R4SC.net/building#InfrastructuralElement"/> </rdfs:Class></rdf:RDF>

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Combining instances and vocabulary

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix b: <http://www.R4SC.net/building#> . @prefix c: <http://www.R4SC.net/city#> .

b:InfrastructuralElementrdf:type rdfs:Class .

b:Buildingrdf:type rdfs:Class ;rdfs:subClassOf b:InfrastructuralElement .

b:hasRoomrdf:type rdf:Property ;rdfs:range b:Room ;rdfs:domain b:Building .

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<http://www.R4SC.net/today#building_1> b:hasRoom <http://www.R4SC.net/today#room_1>; b:hasName “Our summer school building"; c:partOfCity <http://cities.com/#cercedilla> .



Example TTL graph

-> unambiguous / meaningful semantics


93

Index








94




So, it’s also just an RDF graph…

95


We stick to Turtle today

Let’s just quietly extend towards SPARQL as well


96

Index







What is SPARQL

• SPARQL stands for SPARQL Protocol and RDF Query Language• SPARQL is a Query Language• Find the W3C Recommendation page:

http://www.w3.org/TR/rdf-sparql-query/– Used to express queries across diverse data sources, whether the data is

stored natively as RDF or viewed as RDF via middleware. – SPARQL contains capabilities for querying required and optional graph

patterns along with their conjunctions and disjunctions. – SPARQL supports extensible value testing and constraining queries by

source RDF graph. – The results of SPARQL queries can be results sets or RDF graphs.

http://www.w3.org/TR/rdf-sparql-query/

http://www.w3.org/TR/rdf-sparql-query/


The inspiration: SQL

select A1, A2, ..., Anfrom r1, r2, ..., rmwhere P


SPARQL template

prefix a:…select conceptsfrom datasourceswhere { statements }order by …


Structure of a SPARQL query

• Prefix declarationsUsed to abbreviate URIs

• Dataset definitionUsed to state what RDF graph(s) are being queried

• A result clauseUsed to identify what information to return from the

query• The query pattern

Used to specify what to query for in the underlying dataset• Query modifiers, slicing, ordering, and otherwise

Used to rearrange query results (post-processing)


Let’s query our example graph


Example SPARQL Query

PREFIX b: <http://www.R4SC.net/building#> .PREFIX c: <http://www.R4SC.net/city#> .

SELECT ?city2 WHERE {

?b b:hasRoom <http://www.R4SC.net/today#room_1> . ?b c:partOfCity ?city .?city c:closeToCity ?city2

}

variable

Regular RDF statements

Regular RDF prefix declarations


Processing the WHERE statement section

• A pattern is matched against the RDF data• “find a set of bindings such that the substitution of variables for values creates a triple that is in the set of triples making up the graph”

• Source: http://www.w3.org/2004/Talks/17Dec-sparql/QueryLang1/all.html

http://www.w3.org/2004/Talks/17Dec-sparql/QueryLang1/all.html




Graph matching


The Query Result

city2

<http://cities.com/#madrid>


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Example SPARQL endpoint on DBPedia

The HTTP Address of the endpoint

The software used in the server to store the triples (cfr. DBMS)

Diverse options to set


Try it

Try it out on the DBPedia dataset:

http://dbpedia.org/sparql

Or even better: host one yourself and make it available

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– The basis– The SPARQL endpoint– More details



Matching literals (1)

RDF data:@prefix b: <http://www.R4SC.net/building#> . @prefix people: <http://www.R4SC.net/people#> . @prefix xsd: <http://www.w3.org/2001/XMLSchema#> . <http://www.R4SC.net/today#room_1>

b:hasPersonInside "Pieter"@en . <http://www.R4SC.net/today#restaurant>

b:hasPersonInside "Raul"^^xsd:string . <http://www.R4SC.net/today#airport>

b:hasPersonInside "Leandro"^^people:keynotespeaker .

QuerySELECT ?v WHERE { ?v ?p "Pieter" }

Result{ }







QuerySELECT ?v WHERE { ?v ?p "Pieter"@en}

Result{ <http://www.R4SC.net/today#room_1> }







QuerySELECT ?v WHERE { ?v ?p "Leandro"^^< http://www.R4SC.net/people#keynotespeaker > }

Result{ <http://www.R4SC.net/today#airport > }


Querying blank nodes

RDF data:@prefix b: <http://www.R4SC.net/building#> .

_:room1 b:hasPersonInside “Pieter" . _:room2 b:hasPersonInside “Raul" .

QueryPREFIX b: <http://www.R4SC.net/building#> SELECT ?x ?nameWHERE { ?x b:hasPersonInside ?name }

Resultx name

_:c "Pieter"

_:d "Leandro"

x name

_:r "Pieter"

_:s "Leandro"…


CONSTRUCT queriesRDF data:@prefix b: <http://www.R4SC.net/building#> .@prefix : <http://www.R4SC.net/today#> ._:a b:presenterName “Pieter" ._:b b:presenterName “Raul" .:room1 b:hasPersonInside _:a . :room1 b:hasPersonInside “Raul" .:room1 rdf:type b:R4SCPresentationRoom

QueryPREFIX b: <http://www.R4SC.net/building#> WHERE { ?x rdf:type b:R4SCPresentationRoom . ?x: b:hasPersonInside ?z . ?z b:presenterName ?name }CONSTRUCT { ?x b:hasR4SCPresenter ?name }

Result@prefix b: <http://www.R4SC.net/building#> .@prefix : <http://www.R4SC.net/today#> .:room1 b:hasR4SCPresenter “Pieter” .:room1 b:hasR4SCPresenter “Raul”


SPARQL FiltersRDF data:@prefix b: <http://www.R4SC.net/building#> .@prefix : <http://www.R4SC.net/today#> .:room_1 b:hasPresentationTitle “RDF(S) and SPARQL" .:room_1 b:hasPeopleInside 28 .:room_2 b:hasPresentationTitle “Handson session RDF(S) and SPARQL" .:room_2 b:hasPeopleInside 23 .

Query@prefix b: <http://www.R4SC.net/building#> .SELECT ?titleWHERE { ?x b:hasPresentationTitle ?title

FILTER regex(?title, "^Hands") }

Result

title

"Handson session RDF(S) and SPARQL"

Many possibilities: string matching, value restrictions (greaterThan, etc.), DateTime restrictions, …


OPTIONAL keywordRDF data:@prefix b: <http://www.R4SC.net/building#> .@prefix : <http://www.R4SC.net/today#> .:room_1 b:hasPresentationTitle “RDF(S) and SPARQL" .:room_1 b:hasPeopleInside 28 .:room_2 b:hasPresentationTitle “Handson session RDF(S) and SPARQL" .:room_2 b:hasPeopleInside 23 .

Query@prefix b: <http://www.R4SC.net/building#> .SELECT ?title ?attendeesWHERE { ?x b:hasPresentationTitle ?title . OPTIONAL { ?x b:hasPeopleInside ?attendees. FILTER (?attendees > 25) } }

Result

title attendees

"RDF(S) and SPARQL" 28

"Handson session RDF(S) and SPARQL"

If there is a match, give the optional data, otherwise give the required data


LIMIT Keyword

RDF data:@prefix b: <http://www.R4SC.net/building#> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .<http://www.R4SC.net/today#room_1>

b:hasPersonInside “PieterPauwels" , “RaulGarciaCastro" , “AsuncionGomezPerez" , “MariaPovedaVillalon", “FilipRadulovic" .

QueryPREFIX b: <http://www.R4SC.net/building#>SELECT ?nameWHERE { ?x b:hasPersonInside ?name }LIMIT 2

Result

name

“PieterPauwels"

“RaulGarciaCastro"


ORDER BY

RDF data:@prefix b: <http://www.R4SC.net/building#> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .<http://www.R4SC.net/today#room_1>

b:hasPersonInside “PieterPauwels" , “RaulGarciaCastro" , “AsuncionGomezPerez" , “MariaPovedaVillalon", “FilipRadulovic" .

QueryPREFIX b: <http://www.R4SC.net/building#>SELECT ?nameWHERE { ?x b:hasPersonInside ?name }LIMIT 2 ORDER BY DESC(?name)

Result

name

“RaulGarciaCastro"

“PieterPauwels"


DISTINCT KeywordRDF data:@prefix b: <http://www.R4SC.net/building#> .@prefix : <http://www.R4SC.net/today#> .:room_1 b:hasPresentation [ b:hasPresentationTitle “RDF(S) and SPARQL" ] .:room_1 b:hasPresentation [ b:hasPresentationTitle “Handson session Generate your RDF”; b:startsAt “14:30:00”^^xsd:time ] .:room_1 b:hasPresentation [ b:hasPresentationTitle “Handson session Generate your RDF”; b:startsAt “17:00:00”^^xsd:time ] .

QueryPREFIX b: < http://www.R4SC.net/building# >SELECT DISTINCT ?titleWHERE { ?x b:hasPresentationTitle ?title}

Result

title

“RDF(S) and SPARQL"

“Handson session Generate your RDF"


UNION KeywordRDF data:@prefix b: <http://www.R4SC.net/building#> .@prefix : <http://www.R4SC.net/today#> .:room_1 b:hasPresentation [ b:hasPresentationTitle “RDF(S) and SPARQL" ] .:room_1 b:hasPresentation [ b:hasPresentationTitle “Handson session Generate your RDF”; b:startsAt “14:30:00”^^xsd:time ] .:room_1 b:hasPresentation [ b:hasPresentationTitle “Handson session Generate your RDF”; b:startsAt “17:00:00”^^xsd:time ] ._:x1 b:presentation “Linking Data” .

Query@prefix b: <http://www.R4SC.net/building#> .@prefix : <http://www.R4SC.net/today#> .

SELECT DISTINCT ?title_1 ?title_2WHERE { { ?p b:hasPresentationTitle ?title_1 } UNION { ?p1 b:presentation ?title_2 } }

title

“RDF(S) and SPARQL"

“Handson session Generate your RDF"

“Linking Data”

Result


But well, the only way to learn it…

Try it out, for example, on the DBPedia dataset:


Or even better: host one yourself and make it available

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1st Summer School on Smart Cities and Linked Open Data (LD4SC-15)

Thank you for your attention!

[email protected]

Documents

Summer School LD4SC 2015 - RDF(S) and SPARQL