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lecture 8: owl – language I

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OWL XML/RDF syntax: header

<rdf:RDF 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/XLMSchema#">

an OWL ontology may start with a collection of assertions for housekeeping purposes using owl:Ontology element

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owl:Ontology<owl:Ontology rdf:about=""> <rdfs:comment>An example OWL ontology </rdfs:comment> <owl:priorVersion

rdf:resource="http://www.mydomain.org/uni-ns-old"/> <owl:imports

rdf:resource="http://www.mydomain.org/persons"/> <rdfs:label>University Ontology</rdfs:label></owl:Ontology>

…

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owl:Ontologyowl:imports means an ontology O1 imports another ontology O2, and then the entire set of declarations in O2 is appended to O1

importing ontology O2 will also import all of the ontologies that O2 imports

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classesclasses are defined using owl:Class owl:Class is a subclass of rdfs:Class

<owl:Class rdf:about="#associateProfessor”/>

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classes (2)disjointness of classes is defined using owl:disjointWith

<owl:Class rdf:about="#associateProfessor"> <owl:disjointWith rdf:resource="#professor"/> <owl:disjointWith rdf:resource="#assistantProfessor"/></owl:Class>

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classes (3) owl:equivalentClass defines equivalence of classes

<owl:Class rdf:ID="faculty"> <owl:equivalentClass rdf:resource="#academicStaffMember"/></owl:Class>

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classes (4) owl:Thing is the most general class, which contains everything

owl:Nothing is the empty class

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propertiesin OWL there are two kinds of properties object properties, which relate objects to other objectsfor example, is-TaughtBy, supervises

data type properties, which relate objects to datatype valuesfor example, phone, title, age

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datatype propertiesOWL makes use of XML Schema data types, using the layered architecture of the Semantic Web

<owl:DatatypeProperty rdf:ID="age"> <rdfs:range rdf:resource= "http://www.w3.org/2001/XLMSchema

#nonNegativeInteger"/></owl:DatatypeProperty>

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object propertiesuser-defined data types

<owl:ObjectProperty rdf:ID="isTaughtBy"> <owl:domain rdf:resource="#course"/> <owl:range rdf:resource="#academicStaffMember"/> <rdfs:subPropertyOf rdf:resource="#involves"/></owl:ObjectProperty>

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property restrictionsintroduction – anonymous superclass

in OWL we can declare that the class C satisfies certain conditions all instances of C satisfy the conditions

this is equivalent to saying that C is subclass of a class C', where C' collects all objects that satisfy the conditions C' can remain anonymous

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property restrictionsintroduction – anonymous superclass

a (restriction) class is achieved through an owl:Restriction element

this element contains an owl:onProperty element and one or more restriction declarations

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property restrictionsintroduction – anonymous superclass

1 <owl:Class rdf:about=C>2 …3 <rdfs:subClassOf>4 <owl:Restriction>5 <owl:onProperty rdf:resource=P/>6 … declaration of restriction R …7 </owl:Restriction>8 </rdfs:subClassOf>9 …10 </owl:Class> in

Set Theory

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property restrictionsintroduction – anonymous superclass

lines 4 to 7 define the (unnamed) class fo all things that satisfy R

line 3 indicates that C is a sublass of such a (unnamed class)

the pattern in lines 3 to 8 may be repeated to define multiple restrictions for the same class

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property restrictions (2)

three types of restrictions: quantified restrictions value restrictions (filler information) cardinality restrictions

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property restrictions (3)quantified restrictions owl:allValuesFrom specifies universal quantification (C P.D)

owl:someValuesFrom specifies existential quantification (C P.D)

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property restrictions (4)value restrictions owl:hasValue specifies a specific value

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property restrictions (5)cardinality restrictions owl:cardinality specifies the exact number of occurences of P each instance of C must have

owl:maxCardinality (owl:minCardinality)specifies the max (min) number of occurences of P each instance of C must have

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owl:someValuesFrom<owl:Class rdf:about="#academicStaffMember"><rdfs:subClassOf> <owl:Restriction>

<owl:onProperty rdf:resource="#teaches"/><owl:someValuesFrom

rdf:resource="#undergraduateCourse"/> </owl:Restriction></rdfs:subClassOf>

</owl:Class>

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owl:allValuesFrom<owl:Class rdf:about="#firstYearCourse"> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#isTaughtBy"/>

<owl:allValuesFrom rdf:resource=”#professor"/> </owl:Restriction> </rdfs:subClassOf>

</owl:Class>

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owl:hasValue<owl:Class rdf:about="#mathCourse">

<rdfs:subClassOf><owl:Restriction>

<owl:onProperty rdf:resource="#isTaughtBy"/>

<owl:hasValue rdf:resource="#949352"/></owl:Restriction>

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

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cardinality restrictions

<owl:Class rdf:about="#course"> <rdfs:subClassOf><owl:Restriction><owl:onProperty rdf:resource="#isTaughtBy"/><owl:Cardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:Cardinality></owl:Restriction> </rdfs:subClassOf></owl:Class>

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properties of object properties

owl:TransitivePropertyfor example, “has better grade than”, “is ancestor of”

R is transitive iff,for any x, y and z, if R(x,y) and R(y,z) then R(x,z)

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properties of object properties (2)

owl:SymmetricPropertyfor example, “has same grade as”, “is sibling of”

R is symmetric iff,for any x, y, R(x,y) iff R(y,x)

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properties of object properties (3)

owl:FunctionalProperty defines a property that has at most one value for each objectfor example, “age”, “height”, “directSupervisor”

R is functional iff,for any x, y and z, if R(x,y) and R(x,z) then y=z

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properties of object properties (4)

owl:InverseFunctionalProperty defines a property for which two different objects cannot have the same value

R is inverse functional iff,for any x, y and z, if R(y,x) and R(z,x) then y=z

(only for OWL Full)

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properties of object properties (5)

owl:InverseOf

S is the inverse of R iff,for any x, y, R(x,y) iff S(y,x)

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properties of object properties – example

<owl:ObjectProperty rdf:ID=”isTaughtBy">

<rdf:type rdf:resource="&owl;FunctionalProperty"/> <owl:domain rdf:resource="#course"/> <owl:range rdf:resource="#academicStaffMember"/></owl:ObjectProperty>

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properties of object properties – example

<owl:ObjectProperty rdf:ID="hasSameGradeAs">

<rdf:type rdf:resource="&owl;TransitiveProperty"/>

<rdf:type rdf:resource="&owl;SymmetricProperty"/>

<rdfs:domain rdf:resource="#student"/><rdfs:range rdf:resource="#student"/>

</owl:ObjectProperty>

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<owl:ObjectProperty rdf:ID="teaches"> <rdfs:range rdf:resource="#course"/> <rdfs:domain rdf:resource="#academicStaffMember"/> <owl:inverseOf rdf:resource="#isTaughtBy"/></owl:ObjectProperty>

properties of object properties – example

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owl:equivalentProperty

<owl:ObjectProperty rdf:ID="lecturesIn"> <owl:equivalentProperty rdf:resource="#teaches"/></owl:ObjectProperty>

properties of object properties – example