OWL TUTORIAL

APT CSA 3003 OWL ANNOTATOR

Charlie AbelaCSAI Department

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Outline

Ontologies Web Ontology Language: OWL Flavours of OWL Some Differences Classes Properties Individuals Namespaces and Headers

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Ontologies Ontologies were developed in Artificial Intelligence

to facilitate knowledge sharing and reuse. Ontologies provide a machine-processable

semantics of information sources that can be communicated between different agents

An ontology is a formal, explicit specification of a shared conceptualisation [Gruber, 1993] A ‘conceptualisation’ refers to an abstract model of

some phenomenon in the world which identifies the relevant concepts of that phenomenon.

‘Explicit’ means that the type of concepts used and the constraints on their use are explicitly defined.

‘Formal’ refers to the fact that the ontology should be machine readable.

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OWL Web Ontology Language is a language for

defining and instantiating Web ontologies OWL is intended to provide a language that

can be used to describe the classes and relations (properties) between them that are inherent in Web documents and applications.

OWL has more facilities for expressing meaning and semantics than XML, RDF, and RDF-S Reasoning capabilities provided by tools

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Flavours of OWL OWL Lite supports those users primarily

needing a classification hierarchy and simple constraint features

OWL DL supports those users who want the maximum expressiveness without losing computational completeness and decidability of reasoning systems

OWL Full is meant for users who want maximum expressiveness and the syntactic freedom of RDF with no computational guarantees

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Some Differences OWL Lite supports cardinality constraints, but it

only permits cardinality values of 0 or 1 In OWL Lite and OWL DL an individual can never

be at the same time a class: classes and individuals form disjoint domains

In OWL Lite there is no support for boolean constructors, unionOf (OR) and complementOf (not). Some limited support for intersectionOf (AND)

In OWL Lite there is no support for one of (EnumeratedClass) constructor.

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Class Descriptions A class identifier (a URI reference)

<owl:Class rdf:ID="Human"/> A property restriction: value

Universal Quantifier (Class of all individuals whose Parents are Human)

<owl:Restriction> <owl:onProperty rdf:resource="#hasParent" /> <owl:allValuesFrom rdf:resource="#Human"/</owl:Restriction> Existential Quantifier (Class of individuals who have at least one parent a Physician)

<owl:Restriction> <owl:onProperty rdf:resource="#hasParent" /> <owl:someValuesFrom rdf:resource="#Physician" /> </owl:Restriction>

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Class Descriptions (2) A property restriction: cardinality

<owl:Restriction> <owl:onProperty rdf:resource="#hasParent" />

<owl:maxCardinality rdf:datatype="&xsd;nonNegativeInteger">2</owl:maxCardinality></owl:Restriction>

Other constructs: minCardinality and cardinality The intersectionOf two or more class

descriptions <owl:Class rdf:ID="Woman">

<owl:intersectionOf rdf:parseType="Collection"> <owl:Class rdf:about="#Female"/> <owl:Class rdf:about="#Human"/>

</owl:intersectionOf> </owl:Class/>

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Class Axioms Class descriptions form the building blocks for defining

classes through class axioms: rdfs:subClassOf owl:equivalentClass

<owl:Class rdf:about="#Opera"> <rdfs:subClassOf>

<owl:Restriction> <owl:onProperty rdf:resource="#hasLibrettist" />

<owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:minCardinality>

</owl:Restriction> </rdfs:subClassOf> </owl:Class>

<owl:Class rdf:about="#US_President"> <owl:equivalentClass rdf:resource="#ResidentOfWhiteHouse"/></owl:Class>

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Properties OWL distinguishes between two

types of properties:Object properties: have a value range

of class individuals, and thus link individuals to individuals.

Datatype properties have a value range of data values, and thus link individuals to data values.

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Properties (2)<owl:ObjectProperty rdf:ID="course">

<rdfs:domain rdf:resource="#Meal" />

<rdfs:range rdf:resource="#MealCourse" /> </owl:ObjectProperty>

<owl:DatatypeProperty rdf:ID="yearValue"> <rdfs:domain rdf:resource="#VintageYear" /> <rdfs:range rdf:resource="&xsd;positiveInteger"/> </owl:DatatypeProperty>

<owl:ObjectProperty rdf:ID="hasMother"> <rdfs:subPropertyOf rdf:resource="#hasParent"/> </owl:ObjectProperty>

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Property CharacteristicsinverseOf

<owl:ObjectProperty rdf:ID="hasChild"> <owl:inverseOf rdf:resource="#hasParent"/>

</owl:ObjectProperty>

FunctionalProperty: is a property that can have only one(unique) value y for each instance x.

<owl:ObjectProperty rdf:ID="husband"> <rdf:type rdf:resource="&owl;FunctionalProperty" /> <rdfs:domain rdf:resource="#Woman" /> <rdfs:range rdf:resource="#Man" />

</owl:ObjectProperty> ( a Woman can have only one husband)

InverseFunctionalProperty: where a range value uniquelydetermines the domain value

<owl:InverseFunctionalProperty rdf:ID="biologicalMotherOf"> <rdfs:domain rdf:resource="#Woman"/> <rdfs:range rdf:resource="#Human"/>

</owl:InverseFunctionalProperty> (every human has only one biological mother)

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Logical Property Characteristicsowl:TransitiveProperty:

P(x,y) and P(y,z) implies P(x,z)

<owl:TransitiveProperty rdf:ID="subRegionOf"> <rdfs:domain rdf:resource="#Region"/> <rdfs:range rdf:resource="#Region"/>

</owl:TransitiveProperty>

owl:SymmetricProperty: P(x,y) iff P(y,x)

<owl:SymmetricProperty rdf:ID="friendOf"> <rdfs:domain rdf:resource="#Human"/> <rdfs:range rdf:resource="#Human"/>

</owl:SymmetricProperty>

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IndividualsIndividual axioms are statements about individuals,indicating class membership and statements aboutrelevant properties

<Opera rdf:ID="Tosca"> <hasComposer rdf:resource="#Giacomo_Puccini"/> <hasLibrettist rdf:resource="#Victorien_Sardou"/> <hasLibrettist rdf:resource="#Giuseppe_Giacosa"/> <hasLibrettist rdf:resource="#Luigi_Illica"/> <premiereDate rdf:datatype="&xsd;date">1900-01-

14</premiereDate> <premierePlace rdf:resource="#Roma"/> <numberOfActs

rdf:datatype="&xsd;positiveInteger">3</numberOfActs></Opera>

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Individual Identity On the web it is not possible to have unique

names for different things. OWL provides three constructs for making

statements about the identity of individuals: owl:sameAs is used to state that two URI

references refer to the same individual. The construct owl:sameIndividualAs is a synonym of owl:sameAs

owl:differentFrom is used to state that two URI references refer to different individuals

owl:AllDifferent provides an idiom for stating that a list of individuals are all different.

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Individual Identity (2)<Wine rdf:ID="MikesFavoriteWine">

<owl:sameAs rdf:resource="#StGenevieveTexasRed" /></Wine>

<WineSugar rdf:ID="Sweet"> <owl:differentFrom rdf:resource="#Dry"/>

</WineSugar>

<owl:AllDifferent> <owl:distinctMembers rdf:parseType="Collection"> <vin:WineColor rdf:about="#Red" />

<vin:WineColor rdf:about="#White" /> <vin:WineColor rdf:about="#Rose" />

</owl:distinctMembers> </owl:AllDifferent>

owl:distinctMembers can only be used in combination withowl:AllDifferent

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Namespaces<rdf:RDF

xmlns ="http://www.w3.org/TR/………../wine#" xmlns:vin ="http://www.w3.org/TR/……/wine#" xml:base ="http://www.w3.org/TR/……./wine#" xmlns:food="http://www.w3.org/TR/….../food#" xmlns:owl ="http://www.w3.org/2002/07/owl#" xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:xsd ="http://www.w3.org/2001/XMLSchema#">

Abbreviations can be defined using an ENTITY definition

<!DOCTYPE rdf:RDF [ <!ENTITY vin "http://www.w3.org/TR/………/wine#"<!ENTITY food "http://www.w3.org/TR/……../food#" > ]>

<rdf:RDF xmlns ="&vin;" xmlns:vin ="&vin;" xml:base ="&vin;" xmlns:food="&food;" …….>

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Headers

<owl:Ontology rdf:about=""> <rdfs:comment>Example OWL ontology</rdfs:comment> <owl:priorVersionrdf:resource="http://www.w3.org/../wine"/> <owl:imports rdf:resource="http://www.w3.org/……/food"/> <rdfs:label>Wine Ontology</rdfs:label>

……….</owl:Ontology>

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Importing Ontologies owl:imports: references another OWL

ontology containing definitions, whose meaning is considered to be part of the meaning of the importing ontology.

If an OWL Lite ontology imports an OWL DL or OWL Full ontology, it effectively becomes an OWL DL or OWL Full ontology.

If ontology A imports B, and B imports C, then A imports both B and C