Web Ontology Language: OWL had to specify that the literal“l"”isto as a non NegativeInteger (instead of, say, a string), and that we used the xsd namespace declaration made in the header element to refer to the xml Schema document Or we might specify that, for practical reasons, a department must hav at least ten and at <owl: Class rdf: about=#department"> l: Restriction> <owl: onProperty rdf: resource=#hasMember"/> <owl: minCardinality rdf datatype=&xsd; nonNegativeInteger"> </owl: minCardinality> <owl: maxCardinality rdf datatype="&xsd; nonNegativeInteger> </owl: Restriction </rdfs: subClassOf> It is possible to specify a precise number. For example, a PhD student must have exactly two supervisors. This can be achieved by using the same owl: minCardinality and owl: maxCardinality. For convenience, OWL of- fers also owl: cardinality. We conclude by noting that owl: Restriction defines an anonymous class which has no id, is not defined by owl: Class and has only a local scope: it can only be used in the one place where the restriction appears. When we tall bout classes please bare in mind the twofold meaning: classes that are defined by owl: Class with an id, and local anonymous classes as collections of objects that satisfy certain restriction conditions, or as combinations of other classes as we will see shortly. The latter are sometimes called class expressions Special properties erties of property elements can be defined owl: TransitiveProperty defines a transitive property, such as"has bet- ter grade than”," "is taller than',“ is ancestor of”etc owl: SymmetricProperty defines a symmetric property, such as"has same grade as"', "is sibling of", etc owl: FunctionalProperty defines a property that has at most one unique value for each object, such as"age", "height","direct Supervisor"etc owl: Inverse FunctionalProperty defines a property for which two dif- ferent objects cannot have the same value, for example the property"is- TheSocialSecurity Numberfor"(a social security number is assigned to one person onlyWeb Ontology Language: OWL 11 Notice that we had to specify that the literal “1” is to be interpreted as a nonNegativeInteger (instead of, say, a string), and that we used the xsd namespace declaration made in the header element to refer to the XML Schema document. Or we might specify that, for practical reasons, a department must have at least ten and at most thirty members. <owl:Class rdf:about="#department"> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#hasMember"/> <owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger"> 10 </owl:minCardinality> <owl:maxCardinality rdf:datatype="&xsd;nonNegativeInteger"> 30 </owl:maxCardinality> </owl:Restriction> </rdfs:subClassOf> </owl:Class> It is possible to specify a precise number. For example, a PhD student must have exactly two supervisors. This can be achieved by using the same number in owl:minCardinality and owl:maxCardinality. For convenience, OWL of￾fers also owl:cardinality. We conclude by noting that owl:Restriction defines an anonymous class which has no id, is not defined by owl:Class and has only a local scope: it can only be used in the one place where the restriction appears. When we talk about classes please bare in mind the twofold meaning: classes that are defined by owl:Class with an id, and local anonymous classes as collections of objects that satisfy certain restriction conditions, or as combinations of other classes, as we will see shortly. The latter are sometimes called class expressions. Special properties Some properties of property elements can be defined directly: • owl:TransitiveProperty defines a transitive property, such as “has bet￾ter grade than”, “is taller than”, “is ancestor of” etc. • owl:SymmetricProperty defines a symmetric property, such as “has same grade as”, “is sibling of”, etc. • owl:FunctionalProperty defines a property that has at most one unique value for each object, such as “age”, “height”, “directSupervisor” etc. • owl:InverseFunctionalProperty defines a property for which two dif￾ferent objects cannot have the same value, for example the property “is￾TheSocialSecurityNumberfor” (a social security number is assigned to one person only)