The OWL ontology language

1
The OWL ontology language
2
Overview

• The OWL ontology language
• Lite, DL, Full
• RDFS, RDF
• XML, XML namespaces

3
Not yet a semantic web

• Still at RD level
• W3C
• CIRCA (Conceptual Information Retrieval and
  Communication Architecture)
• CYC (Cycorp, www.cyc.com)
• Development of base technology
• Editors
• Translators
• Reasoners

4
Problems with semantic web

• Limited precision and recall of search engines
• Maintaining reputable and reliable directories of
  services
• Complexity in exchanges, message types and roles
  played by agents
• Semantic heterogeneity

5
Ontology languages

• UML
• Rich representational system, widely used, well
  suited to represent ontology elements
• Unable to specify instances, not intended for
  public use or to be combined into larger
  ontologies.
• RDF
• Can represent instances, XML-based, has fine
  level of granularity
• No convenient mechanism to represent ontology as
  engineered object, limited use of properties
• OWL

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OWL

• Family of formalisms to represent ontologies
• Endorsed by W3C
• Three versions
• Lite
• DL
• Full
• Built on top of RDFS
• Not intended to be written by humans

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XML

• Mark up language to store and transport data
• Similar to HTML but tags have to be defined
• Based on tree structure
• Entities declaration
• Defines abbreviations for terms used in attribute
  values
• Namespaces
• Method to avoid name conflicts, used in element
  (tag) names
• Datatypes

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XML tree structure
ltbookstoregt ltbook category"COOKING"gt lttitle
lang"en"gtEveryday Italianlt/titlegt
ltauthorgtGiada De Laurentiislt/authorgt
ltyeargt2005lt/yeargt ltpricegt30.00lt/pricegt
lt/bookgt ltbook category"CHILDREN"gt lttitle
lang"en"gtHarry Potterlt/titlegt ltauthorgtJ K.
Rowlinglt/authorgt ltyeargt2005lt/yeargt
ltpricegt29.99lt/pricegt lt/bookgt lt/bookstoregt
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Elements and attributes

• As element
• ltpersongt
• ltsexgtfemalelt/sexgt
• ltfirstnamegtAnnalt/firstnamegt
• ltlastnamegtSmithlt/lastnamegt
• lt/persongt
• As attribute
• ltperson sex"female"gt
• ltfirstnamegtAnnalt/firstnamegt
• ltlastnamegtSmithlt/lastnamegt
• lt/persongt

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Entities

• Can be used for abbreviating references to URIs
• lt!ENTITY name full URI"gt
• Referenced in attributes by enclosing them
  within and
• lt!ENTITY pizza
• "http//www.co-ode.org/ontologies/pizza/pizza.owl
  " gt
• ltOWLClass URI"pizzaFourSeasons"/gt
• ltOWLClass URI"pizzaParmense"/gt

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Namespaces
ltrootgt lthtable xmlnsh"http//www.w3.org/TR/html
4/"gt lthtrgt lthtdgtAppleslt/htdgt
lthtdgtBananaslt/htdgt lt/htrgt lt/htablegt ltftable
xmlnsf"http//www.w3schools.com/furniture"gt
ltfnamegtCoffee Tablelt/fnamegt ltfwidthgt80lt/fwidt
hgt ltflengthgt120lt/flengthgt lt/ftablegt lt/rootgt
ltrootgt lttablegt lttrgt lttdgtAppleslt/tdgt
lttdgtBananaslt/tdgt lt/trgt lt/tablegt lttablegt
ltnamegtCoffee Tablelt/namegt ltwidthgt80lt/widthgt
ltlengthgt120lt/lengthgt lt/tablegt lt/rootgt
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Datatypes

• Defined as part of XML Schema
• lt!ENTITY xsd "http//www.w3.org/2001/XMLSchema"
  gt
• ltowlDatatypeProperty rdfID"dayOfYear"gt
• ltrdfsdomain rdfresource"DateTimeDescripti
  on" /gt
• ltrdfsrange rdfresource"xsdnonNegativeInt
  eger" /gt
• lt/owlDatatypePropertygt

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RDF

• Resource Description Framework
• Designed to be read and understood by computers
• Provides a framework for describing web resources
  in statements of the form
• Subject, predicate, object or
• Resource, property, value

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RDF example
ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/22-r
df-syntax-ns" xmlnscd"http//www.recshop.fake/
cd"gt ltrdfDescription rdfabout"http//www.rec
shop.fake/cd/Empire Burlesque"gt
ltcdtitlegtEmpire Burlesquelt/cdtitlegt
ltcdartistgtBob Dylanlt/cdartistgt ltcdcountrygtUSAlt/
cdcountrygt ltcdcompanygtColumbialt/cdcompanygt
ltcdpricegt10.90lt/cdpricegt ltcdyeargt1985lt/cdyea
rgt lt/rdfDescriptiongt . lt/rdfRDFgt
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Another example
lt?xml version"1.0"?gt ltrdfRDF
xmlnsrdf"http//www.w3.org/1999/02/22-rdf-syntax
-ns" xmlnslib"http//purl.org/lib/elements
/1.1/"gt ltrdfDescription about"http//www.cs
.rpi.edu/puninj/XMLJ/"gt ltlibcreatorgtJohn
Puninlt/libcreatorgt ltlibtitlegtProgramming
XML in Javalt/libtitlegt ltlibdategt2001-04-1
0lt/libdategt lt/rdfDescriptiongt
ltrdfDescription about"http//www.cs.rpi.edu/pun
inj/XGMML/"gt ltlibcreatorgtJohn
Puninlt/libcreatorgt ltlibtitlegtExtensible
Graph Markup and Modeling Languagelt/libtitlegt
ltlibdategt2001-04-04lt/libdategt
lt/rdfDescriptiongt lt/rdfRDFgt
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RDFS

• Resource Description Framework Schema
• Built on top of RDF
• Provides a framework for describing application
  specific classes and properties
• Resources can be defined as instances of classes
  or subclasses of classes
• Allows the description of class hierarchies as
  well as their individuals

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Combining RDF and RDFS
ltrdfRDF xmlnsrdf "http//www.w3.org/1999/02/22-
rdf-syntax-ns" xmlnsrdfs"http//www.w3.org/200
0/01/rdf-schema" xmlbase "http//www.animals.f
ake/animals"gt ltrdfDescription rdfID"animal"gt
ltrdftype rdfresource"http//www.w3.org/200
0/01/rdf-schemaClass"/gt lt/rdfDescriptiongt ltrdf
Description rdfID"horse"gt ltrdftype
rdfresource"http//www.w3.org/2000/01/rdf-schema
Class"/gt ltrdfssubClassOf rdfresource"animal
"/gt lt/rdfDescriptiongt lt/rdfRDFgt
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Simplifying with RDFS
ltrdfRDF xmlnsrdf "http//www.w3.org/1999/02/22
-rdf-syntax-ns" xmlnsrdfs"http//www.w3.org/20
00/01/rdf-schema" xmlbase "http//www.animals.
fake/animals"gt ltrdfsClass rdfID"animal"
/gt ltrdfsClass rdfID"horse"gt
ltrdfssubClassOf rdfresource"animal"/gt lt/rdfsC
lassgt lt/rdfRDFgt
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So far

• XML
• Tree structure (elements and attributes)
• Entity declarations
• Namespaces
• Datatypes
• RFD
• Statements of the form subject, predicate, object
• RDFS
• Framework for describing hierarchies of classes
  and properties

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OWL

• RDF RDFS do not provide a mechanism for
  specifying restrictions
• Lite class hierarchies, simple restrictions
• DL all inferences can be computed and will
  finish in finite time
• Full classes can be treated both as classes and
  as individuals

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Classes and subclasses
ltrdfRDF xmlnsrdf "http//www.w3.org/1999/02/22
-rdf-syntax-ns" xmlnsrdfs"http//www.w3.org/20
00/01/rdf-schema xmlnsowl"http//www.w3.org/20
02/07/owl"gt xmlbase "http//www.animals.fake/a
nimals"gt ltowlClass rdfID"animal"
/gt ltowlClass rdfID"horse"gt ltrdfssubClassOf
rdfresource"animal"/gt lt/owlClassgt lt/rdfRDFgt
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More OWL, less RDF
ltOntology xmlnsrdf "http//www.w3.org/1999/02/2
2-rdf-syntax-ns" xmlnsrdfs"http//www.w3.org/2
000/01/rdf-schema xmlnsowl"http//www.w3.org/2
002/07/owl"gt xmlbase "http//www.animals.fake/
animals"gt ltDeclarationgt ltOWLClass
URI"animalsanimal"/gt lt/Declarationgt ltSubClassO
fgt ltOWLClass URI"animalshorse"/gt
ltOWLClass URI"animalsanimal"/gt lt/SubClassOfgt
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Another example
ltowlClass rdfabout"Pizza"gt
ltrdfslabelgtPizzalt/rdfslabelgt
ltrdfssubClassOf rdfresource"Food"/gt
ltowldisjointWith rdfresource"PizzaBase"/gt
ltowldisjointWith rdfresource"PizzaTopping"
/gt lt/owlClassgt ltowlClass
rdfabout"PizzaBase"gt
ltrdfslabelgtBaseDaPizzalt/rdfslabelgt
ltrdfssubClassOf rdfresource"Food"/gt lt/owlClas
sgt ltowlClass rdfabout"PizzaTopping"gt
ltrdfssubClassOf rdfresource"Food"/gt lt/owlClas
sgt
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Individuals
ltowlClass rdfabout"Country"gt
ltrdfssubClassOf rdfresource"owlThing"/gt lt/owl
Classgt ltCountry rdfabout"Italy"/gt
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Properties
ltowlObjectProperty rdfabout"hasIngredient"gt
ltrdftype rdfresource"owlTransitivePrope
rty"/gt ltowlinverseOf rdfresource"isIng
redientOf"/gt lt/owlObjectPropertygt ltowlObjectPro
perty rdfabout"hasBase"gt ltrdftype
rdfresource"owlFunctionalProperty"/gt
ltrdftype rdfresource"owlInverseFunctionalProp
erty"/gt ltrdfssubPropertyOf
rdfresource"hasIngredient"/gt
ltowlinverseOf rdfresource"isBaseOf"/gt
lt/owlObjectPropertygt ltowlDatatypeProperty
rdfabout"diameter"gt ltrdftype
rdfresource"owlFunctionalProperty"/gt lt/owlDat
atypePropertygt
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Domains and ranges
ltowlObjectProperty rdfabout"hasTopping"gt
ltrdfsdomain rdfresource"Pizza"/gt
ltrdfsrange rdfresource"PizzaTopping"/gt
ltrdfssubPropertyOf rdfresource"hasIngredient"
/gt ltowlinverseOf rdfresource"isTopping
Of"/gt lt/owlObjectPropertygt ltowlDatatypeProperty
rdfabout"diameter"gt ltrdftype
rdfresource"owlFunctionalProperty"/gt
ltrdfsdomain rdfresource"PizzaBase"/gt
ltrdfsrange rdfresource"xsdnonNegativeInteger"
/gt lt/owlDatatypePropertygt
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Existential restrictions
ltowlClass rdfabout"Pizza"gt
ltrdfslabelgtPizzalt/rdfslabelgt
ltrdfssubClassOf rdfresource"Food"/gt
ltrdfssubClassOfgt ltowlRestrictiongt
ltowlonProperty rdfresource"hasBa
se"/gt ltowlsomeValuesFrom
rdfresource"PizzaBase"/gt
lt/owlRestrictiongt lt/rdfssubClassOfgt
ltowldisjointWith rdfresource"PizzaBase"/gt
ltowldisjointWith rdfresource"PizzaTopp
ing"/gt lt/owlClassgt
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Existential restrictions
ltowlClass rdfabout"CheeseyPizza"gt
ltowlequivalentClassgt
ltowlRestrictiongt ltowlonProperty
rdfresource"hasTopping"/gt
ltowlsomeValuesFrom rdfresource"CheeseTopping"/
gt lt/owlRestrictiongt
lt/owlequivalentClassgt ltrdfssubClassOf
rdfresource"Pizza"/gt lt/owlClassgt
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An alternative syntax
Instant a owlClass
rdfssubClassOf TemporalEntity . Interval
a owlClass rdfssubClassOf
TemporalEntity . TemporalEntity a
owlClass rdfssubClassOf TemporalThing
owlequivalentClass a
owlClass owlunionOf
(Instant Interval) .
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Universal restrictions
ltowlClass rdfabout"VegetarianPizza"gt
ltowlequivalentClassgt
ltowlRestrictiongt
ltowlonProperty rdfresource"hasTopping"/gt
ltowlallValuesFromgt
ltowlClassgt
ltowlunionOf rdfparseType"Collection"
gt
ltrdfDescription rdfabout"VegetableTopping"/gt

ltrdfDescription rdfabout"CheeseTopping"/gt
lt/owlunionOfgt
lt/owlClassgt
lt/owlallValuesFromgt
lt/owlRestrictiongt lt/owlequivalentClassgt
ltrdfssubClassOf rdfresource"Pizza"/gt lt
/owlClassgt
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Closure axiom
ltowlClass rdfabout"MargheritaPizza"gt
ltrdfssubClassOf rdfresource"NamedPizza"/gt
ltrdfssubClassOfgt
ltowlRestrictiongt ltowlonProperty
rdfresource"hasTopping"/gt
ltowlallValuesFromgt
ltowlClassgt ltowlunionOf
rdfparseType"Collection"gt
ltrdfDescription rdfabout"MozzarellaToppi
ng"/gt
ltrdfDescription rdfabout"TomatoTopping"/gt
lt/owlunionOfgt
lt/owlClassgt
lt/owlallValuesFromgt
lt/owlRestrictiongt lt/rdfssubClassOfgt lt/ow
lClassgt
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Cardinality restrictions
ltowlClass rdfabout"DoubleVeggyPizza"gt
ltowlequivalentClassgt ltowlClassgt
ltowlintersectionOf
rdfparseType"Collection"gt
ltowlRestrictiongt
ltowlonProperty rdfresource"hasTopping"/gt
ltowl11onClass
rdfresource"VegetableTopping"/gt
ltowlminCardinality rdfdatatype"xsdno
nNegativeInteger"gt2lt/owlminCardinalitygt
lt/owlRestrictiongt
lt/owlintersectionOfgt
lt/owlClassgt lt/owlequivalentClassgt
ltrdfssubClassOf rdfresource"VegetarianPi
zza"/gt lt/owlClassgt
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Data restrictions
ltowlClass rdfabout"LargePizzaBase"gt
ltowlequivalentClassgt
ltowlRestrictiongt ltowlonProperty
rdfresource"diameter"/gt
ltowlsomeValuesFromgt
ltrdfDescriptiongt
ltrdftype rdfresource"owlDataRange"/gt
ltowl11minInclusive
rdfdatatype"xsdint"gt12lt/owl11minInclusivegt
ltowl11onDataRange
rdfresource"xsdint"/gt
lt/rdfDescriptiongt
lt/owlsomeValuesFromgt
lt/owlRestrictiongt lt/owlequivalentClassgt
ltrdfssubClassOf rdfresource"PizzaBase"
/gt lt/owlClassgt
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Key points

• OWL is built on top of RDFS, RDF and XML
• XML encodes namespaces and data types
• RDF and RDFS encode hierarchies
• OWL (DL) encodes restrictions

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Further reading

• Colomb, R. 2007. Ontology and the semantic web.
  IOS Press.
• Lee W. L. 2005. Owl Representing Information
  Using the Web Ontology Language. Trafford.
• XML tutorial
• http//www.w3schools.com/xml/default.asp
• RDF tutorial
• http//www.w3schools.com/rdf/default.asp
• OWL guide
• http//www.w3.org/TR/owl-guide/