2. semantic web layers - xml and rdf
TRANSCRIPT
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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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???
???
???
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Ontology Languages• Wide variety of languages for “Explicit Specification”
– Graphical notations
• Semantic networks
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Ontology Languages• Wide variety of languages for “Explicit Specification”
– Graphical notations
• Topic Maps
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Ontology Languages• Wide variety of languages for “Explicit Specification”
– Graphical notations
• M!
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Ontology Languages
• Wide variety of languages for “Explicit Specification”
– Graphical notations
• "#$
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Ontology Languages
• Wide variety of languages for “Explicit Specification”
– !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
• Wide variety of languages for “Explicit Specification”
– !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 – $ormal properties well understood &complexity( decida%ility-
– 0nown reasoning algorithms
– *mplemented systems &highly optimised-
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(In)famous “Layer Cake”
≈ Data Exchange
≈ Semantics+reasoning
≈ Relational Data
?
?
???
???
???
• "elationship %etween layers is not clear
• )W! #! extends “#! su%set” of "#$