2. Semantic Web Layers - XML and RDF

8/17/2019 2. Semantic Web Layers - XML and RDF

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Ontology languages, XML and RDF


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Contents

• Definition of ontology•A quick survey to famous ontology languages

• Graphical• Logic based● XML

● XML, namespaces, XL!● XL!, XL"#$

● %D#


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Ontology

• An ontology is a hierarchically structured set of terms for

describing a domain that can be used as a skeletal foundation

for a kno&ledge base' (&artout, )atil, *night, %uss+

• An ontology provides the means for describing eplicitly theconceptuali-ation behind the kno&ledge represented in a

kno&ledge base' (.ernaras, Lasergoiti, /orrera+• An ontology is a formal, eplicit specification of a shared

conceptuali-ation (tuder, .en0amins,#ensel+


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(In)famous “Layer Cake”

≈ Data Exchange

≈ Semantics+reasoning

≈ Relational Data

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Ontology Languages• Wide variety of languages for “Explicit Specification”

– Graphical notations

• Semantic networks


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• Topic Maps


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• M!


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Ontology Languages

• Wide variety of languages for “Explicit Specification”


• "#$


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Ontology Languages


– !ogic %ased

• #escription !ogics &e'g'( )*!( #+M!,)*!( )W!-

• "ules &e'g'( "uleM!( !./.rolog-

• $irst )rder !ogic &e'g'( 0*$-


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Ontology Languages• Wide variety of languages for

“Explicit Specification”

– !ogic %ased

• 1onceptual graphs


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Ontology Languages


– !ogic %ased

• 1onceptual graphs

• &Syntactically- higher order logics &e'g'( !2ase-

• 3on4classical logics &e'g'( $logic( 3on4Mon( modalities-

– 2ayesian/pro%a%ilistic/fu55y

• #egree of formality varies widely

– *ncreased formality makes languages more amena%le to

machine processing &e'g'( automated reasoning-


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• )%6ects /*nstances/*ndividuals – Elements of the domain of discourse

– E7uivalent to constants in $)!

• Types /1lasses/1oncepts – Sets of o%6ects sharing certain characteristics

– E7uivalent to unary predicates in $)!

• "elations /.roperties/"oles – Sets of pairs &tuples- of o%6ects

– E7uivalent to %inary predicates in $)!

• Such languages are/can %e8 – Well understood

– $ormally specified

– &"elatively- easy to use

– +mena%le to machine processing

Many languages use “object oriented” model based on:


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We “!"#ema” Languages

• Existing We% languages extended to facilitate contentdescription

– 9M! 9M! Schema &9M!S-

– "#$ "#$ Schema &"#$S-

• 9M!S not an ontology language – 1hanges format of #T#s &document schemas- to %e 9M!

– +dds an extensi%le type hierarchy

• *ntegers( Strings( etc'

• 1an define su%4types( e'g'( positive integers

• "#$S is recognisa%le as an ontology language

– 1lasses and properties

– Su%/super4classes &and properties-

– "ange and domain &of properties-


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XML

– Unformal definition:

– XML is a markup language for representation of

– documents which contain stuctured information.

•Usages:

Data exchange (e.g. RSS S!"#$en%elope ad hoc &'&data exchange

)e* ser%ices

Data integration

+ontent pu*lishing (single source multiple output

Multimedia presentations (SM,L


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XML

• .rocessing

– .arsing

• S+98 uses call%ack to notify occurences of each

element&e'g' Start#ocument&-( startElement&-(

end#ocument&-( etc'-• #)M8 Makes and o%6ect model of the document in memory

– "emote procedure call8 9M!4".1

– S)+. &we% serices-


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$ames%a"es &n XML

3amespaces avoids name conflicts

• same tag for different things

• same tag for different format

Example8

#ocument :8 ;person


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$ames%a"es &n XML ("ont')

• $irst try Tim Berners Lee

Second try

Tim Berners Lee

Final solution

Tim Berners Lee


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$ames%a"e eam%le

!eorge "oros

$ounting ...

.....


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XML Schema: What is a Schema ?

A schema defnes the content o a number o XML-documents

It defnes

which elements and attributes can be included the element content the order of elements

Schema substitutes DTD

Think o classes (schema) and instances(documents)


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XML Schema

Schema is saved ith !ostf" #"sd A document is validated a$ainst a schema A schema is a XML-document


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XSL9S! consist of

– formatting o%6ects – 9S! Transformations &9S!T-

• $ormatting o%6ect8 specifies presentation

• 9S!T8 Transformations to ar%itrary format

• The idea of 9S!T8 traverse the tree and apply a specific

template at each node

• sage – 9M! to 9M! &i'e' S>G-

– 9M! to &9-?TM!

– 9M! to text

– 9M! to other formats &i'e 1S>-


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The XSLT language

• Transformation in 9M! dialect

• Example8

• + rule %ased language

• )utput handled %y the enviroment


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Terminology

• Template rules consists of8

– pattern

– template

• .attern specifies nodes a template applies to

– tag name

– attri%utes

– context

• Template defines the transformations


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XML Example

chic)en soup

*ntroduction

*+,e lw-s..

book

title section

title para


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Template rule for boo


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Template rule for section


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Formatting ob!ects

• $ormatting represents common document elements

• Example – %lock

– external4graphic

– ta%le – simple4link

• They are specified in 9M!

• +ttri%utes specify their appearance


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Template rule "ith ob!ects


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SM#L

SMIL Synchronized Multimedia Integration Language SMIL is an XML extension

used for multimedia presentations which integratestreaming audio and video with images, text, etc

enables to specify what should be presented when


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SM#L

Introduction !bout XML XML Schema XML

"amespaces XSL# $uture


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SM#L

%smil& %head& %'head&

%bod& %!ar&

%audio src*sound#rm*'& %se+& %te"tstream src*tobbe,#rt* re$ion*videore$ion*'& %!ar&

%te"tstream src*tobbe#rt* re$ion*te"tre$ion*'& %video src*tobias#rm* re$ion*videore$ion*'&

%'!ar& %'se+& %'!ar& %'bod&

%'smil&


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RDF and RDF!

• "#$ stands for "esource #escription $ramework

• *t is a W@1 candidate recommendation

&http8//www'w@'org/"#$-

• "#$ is graphical formalism & , 9M! syntax , semantics-

– for representing metadata

– for descri%ing the semantics of information in a machine4

accessi%le way

• "#$S extends "#$ with “schema voca%ulary”( e'g'8

– 1lass( .roperty

– type( su%1lass)f( su%.roperty)f

– range( domain


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#e RDF Data Model

• Statements are ;su%6ect( predicate( o%6ect< triples8


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+RIs

• "* niform "esource *dentifier

• HThe generic set of all names/addresses that are short

strings that refer to resourcesH

•"!s &niform "esource !ocators- are a particular type of"*( used for resources that can %e accessed on the WWW

&e'g'( we% pages-

• *n "#$( "*s typically look like “normal” "!s( often with

fragment identifiers to point at specific parts of a

document8

– http8//www'somedomain'com/some/path/to/fileIfragment*#


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L&nk&ng !tatements

• The su%6ect of one statement can %e the o%6ect of another

• Such collections of statements form a directed( la%eled

graph

• 3ote that the o%6ect of a triple can also %e a “literal” &a

string-

*nut# !+#asColleague

Carole #tt%--...'stanford'edu

#asColleague#as/ome0age


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/o. "an RDF e &m%lemented

• sally "#$/9M! syntax

• ?owever other notations are possi%le

– e'g' 3otation@

"Sean"


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RDF !ynta

• "#$ has an 9M! syntax that has a specific meaning8

• Every Description element descri%es a resource

• Every attri%ute or nested element inside a Description is a propert- of that "esource

•We can refer to resources %y using "*s

http://www.stn%ord.edu/6th


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Rdf ty%e

• "#$ predifined property

• *ts value J a resource that represent a category or class

• *ts su%6ect J *nstance of that category or class

pre%ix ex :0 7*: http://www.exmple.org/terms


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Rdf "onta&ners

• 2ag8 &+ resource having type rdf82ag-

– "epresents an unordered list of resources or literals

– #uplicated values are prermitted

• Se7uence8 &+ resource having type rdf8Se7-

– "epresents ordered list of resources or literal – #uplicated values are permitted

• +lternatives8 &+ resource having type rdf8+lt-

– "epresents group of resources or literals that are alternatives


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1ag eam%le


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RDF re&f&"at&on

• association of a statement and a specific resourcerepresenting the statement

• used to make statements a%out statements

• >oca%ulary8• type rdf:Statement

• properties

• rdf:subject

• rdf:predicate• rdf:object


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Re&f&"at&on eam%le

• The mem%er of pro6ect opposed the statement thathttp8//www'daml'org/pro6ects/I:: is an 3S$ foundedpro6ect

http://www.daml.org/projects/#11http://www.daml.org/projects/#11


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RDF gra%#s


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RDF !"#ema (RDF!)

• "#$ gives a formalism for meta data annotation( and a wayto write it down in 9M!( %ut it does not give any specialmeaning to voca%ulary such as su%1lass)f or type

– *nterpretation is an ar%itrary %inary relation

• "#$ Schema allows you to define voca%ulary terms and the

relations %etween those terms

– it gives “extra meaning” to particular "#$ predicates and

resources

– this “extra meaning”( or semantics( specifies how a term

should %e interpreted


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RDF! 2am%les•

"#$ Schema terms &6ust a few examples-8 – 1lass

– .roperty

– type

– su%1lass)f

– range – domain

• These terms are the "#$ Schema %uilding %locks

&constructors- used to create voca%ularies8


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RDF! &s aout "reat&ng taonom&es


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*nferences8

Kangt5e is ariver

Kangt5e has a length of L@DD 0ilometers

Inferen"es &n RDF and RDF!


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• Two classes same concept8

– E7uivalent classes8 +irplane and .lane

• 1ardinality constraints8

– )cean has one max#epth

Des&re for more e%ress&3eness


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RDF-RDF! “L&eral&ty”

• 3o distinction %etween classes and instances &individuals-

• .roperties can themselves have properties

• 3o distinction %etween language constructors and

ontology voca%ulary( so constructors can %e applied to

themselves/each other


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RDF! semant&" us&ng log&"


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0rolems .&t# RDF!

• "#$S too weak to descri%e resources in sufficient detail

– 3o localised range and domain constraints

• 1ant say that the range of has1hild is person when

applied to persons and elephant when applied to elephants

– 3o existence/cardinality constraints• 1ant say that all instances of person have a mother that is

also a person( or that persons have exactly = parents

– 3o transitive( inverse or symmetrical properties

• 1ant say that is.art)f is a transitive property( that has.art

is the inverse of is.art)f or that touches is symmetrical – F

• #ifficult to provide reasoning support

– 3o “native” reasoners for non4standard semantics

– May %e possi%le to reason via $) axiomatisation


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RDF(!) tools• "ead "#$ data

– .arsers8 Nena( "edland( SW*4.rolog

– >alidators8 W@1 "#$ validation service

– Editors8 *sa>i5( "#$ +uthor( "#$Ed( *nferEd

• Store "#$ data &9M! format( tripples or relational/oo #2-

– "SS#2( "#$!i%

• se "#$ data &applications( "SS news( etc'-

• Manipulate "#$ data &inference( 7uery( etc'-

– Nena "#O!( etc'

– Example8SE!E1T Bperson( Bknows

W?E"E &Bx ;http8//xmlns'com/foap/knows< B5-(

&Bx ;http8//xmlns'com/foap/name< Bperson-(

&B5 ;http8//xmlns'com/foap/name< Bknows-

http://xmlns.com/foap/knowshttp://xmlns.com/foap/namehttp://xmlns.com/foap/namehttp://xmlns.com/foap/namehttp://xmlns.com/foap/namehttp://xmlns.com/foap/knows


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We Ontology Language Re4u&rements

#esira%le features identified for We% )ntology !anguage8

• Extends existing We% standards

– Such as 9M!( "#$( "#$S

• Easy to understand and use

– Should %e %ased on familiar 0" idioms

• $ormally specified

• )f “ade7uate” expressive power • .ossi%le to provide automated reasoning support


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From RDF to OWL

• Two languages developed to satisfy a%ove re7uirements

– )*!8 developed %y group of &largely- European researchers &several

from E )nto0nowledge pro6ect-

– #+M!4)3T8 developed %y group of &largely- S researchers &in #+".+

#+M! programme-

• Efforts merged to produce #+M!,)*!

– #evelopment was carried out %y “Noint E/S 1ommittee on +gent

Markup !anguages”

– Extends &“#! su%set” of- "#$

• #+M!,)*! su%mitted to W@1 as %asis for standardisation

– We%4)ntology &We%)nt- Working Group formed

– We%)nt group developed )W! language %ased on #+M!,)*!

– )W! language now a W@1 1andidate "ecommendation

– Will soon %ecome .roposed "ecommendation


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OWL Language

• Three species of )W! – )W! full is union of )W! syntax and "#$

– )W! #! restricted to $)! fragment &¼ #+M!,)*!-

– )W! !ite is “easier to implement” su%set of )W! #!

• Semantic layering – )W! #! ¼ )W! full within #! fragment – #! semantics officially definitive

• )W! #! %ased on SHIQ #escription !ogic

– *n fact it is e7uivalent to SHOIN(Dn) #!

• )W! #! 2enefits from many years of #! research – Well defined semantics – $ormal properties well understood &complexity( decida%ility-

– 0nown reasoning algorithms

– *mplemented systems &highly optimised-


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(In)famous “Layer Cake”

≈ Data Exchange

≈ Semantics+reasoning

≈ Relational Data

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???

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• "elationship %etween layers is not clear

• )W! #! extends “#! su%set” of "#$

Documents

2. Semantic Web Layers - XML and RDF