ece 720 intelligent web: ontology and beyond lecture 8: owl – language I

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 ece 720, winter ‘12

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> … ece 720, winter ‘12

owl:Ontology owl: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 ece 720, winter ‘12

classes classes are defined using owl:Class owl:Class is a subclass of rdfs:Class <owl:Class rdf:about="#associateProfessor”/> ece 720, winter ‘12

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> ece 720, winter ‘12

classes (3) owl:equivalentClass defines equivalence of classes <owl:Class rdf:ID="faculty"> <owl:equivalentClass rdf:resource="#academicStaffMember"/> </owl:Class> ece 720, winter ‘12

classes (4) owl:Thing is the most general class, which contains everything owl:Nothing is the empty class ece 720, winter ‘12

properties in OWL there are two kinds of properties object properties, which relate objects to other objects for example, is-TaughtBy, supervises data type properties, which relate objects to datatype values for example, phone, title, age ece 720, winter ‘12

datatype properties OWL 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> ece 720, winter ‘12

object properties user-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> ece 720, winter ‘12

property restrictions introduction – 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 ece 720, winter ‘12

property restrictions introduction – 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 ece 720, winter ‘12

property restrictions introduction – 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 ece 720, winter ‘12

property restrictions introduction – 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 ece 720, winter ‘12

property restrictions (2) three types of restrictions: quantified restrictions value restrictions (filler information) cardinality restrictions ece 720, winter ‘12

property restrictions (3) quantified restrictions owl:allValuesFrom specifies universal quantification (C P.D) owl:someValuesFrom specifies existential quantification (C P.D) ece 720, winter ‘12

property restrictions (4) value restrictions owl:hasValue specifies a specific value ece 720, winter ‘12

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 ece 720, winter ‘12

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> ece 720, winter ‘12

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> ece 720, winter ‘12

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> ece 720, winter ‘12

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> ece 720, winter ‘12

properties of object properties owl:TransitiveProperty for 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) ece 720, winter ‘12

properties of object properties (2) owl:SymmetricProperty for example, “has same grade as”, “is sibling of” R is symmetric iff, for any x, y, R(x,y) iff R(y,x) ece 720, winter ‘12

properties of object properties (3) owl:FunctionalProperty defines a property that has at most one value for each object for 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 ece 720, winter ‘12

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) ece 720, winter ‘12

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) ece 720, winter ‘12

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> ece 720, winter ‘12

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> ece 720, winter ‘12

properties of object properties – example <owl:ObjectProperty rdf:ID="teaches"> <rdfs:range rdf:resource="#course"/> <rdfs:domain rdf:resource="#academicStaffMember"/> <owl:inverseOf rdf:resource="#isTaughtBy"/> </owl:ObjectProperty> ece 720, winter ‘12

properties of object properties – example owl:equivalentProperty <owl:ObjectProperty rdf:ID="lecturesIn"> <owl:equivalentProperty rdf:resource="#teaches"/> </owl:ObjectProperty> ece 720, winter ‘12