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Property features are defined by the property axioms. The basic form expresses the existence only. For example,
in a smartphone ontology, the property
hasTouchscreen
can be declared to express a major feature of mobile phones
(see Listing 7-76).
Listing 7-76.
A Property Declaration in OWL
<owl:ObjectProperty rdf:ID="hasTouchscreen"/>
OWL property axioms can also define additional characteristics. OWL supports RDF Schema constructs
such as
rdfs:subPropertyOf
,
rdfs:domain
, and
rdfs:range
. Relations to other properties can be expressed by
owl:equivalentProperty
and
owl:inverseOf
(Listing 7-77).
Listing 7-77.
Two Equivalent Smartphone Properties (Accelerometer and G-sensor)
<owl:ObjectProperty rdf:ID="hasAccelerometer">
<owl:equivalentProperty>
<owl:ObjectProperty rdf:ID="hasGsensor"/>
</owl:equivalentProperty>
</owl:ObjectProperty>
Global cardinality constraints are defined by
owl:FunctionalProperty
and
owl:InverseFunctionalProperty
.
Logical property features are defined by
owl:SymmetricProperty
and
owl:TransitiveProperty
[158] (Listing 7-78).
Listing 7-78.
A Symmetric Property in OWL
<owl:SymmetricProperty rdf:ID="hasLiveConnection">
<rdfs:domain rdf:resource="#Smartphone"/>
<rdfs:range rdf:resource="#Smartphone"/>
</owl:SymmetricProperty>
OWL provides precise declarations for expressing relationships, even if they are evident. For example, the
property hierarchy
of two smartphone features can be expressed in functional syntax, as presented in Listing 7-79.
Listing 7-79.
Property Hierarchy in OWL
SubObjectPropertyOf( :hasGeotagging :hasCamera )
Classes
Similar to RDF, OWL provides classes to group resources. There are six different
class descriptions
in OWL:
•
Class identifier (URI reference). A named instance of
owl:Class
, a subclass of
rdfs:Class
.
8
Listing 7-80 shows an example.
Listing 7-80.
A Class Identifier in OWL
<owl:Class rdf:ID="Handheld"/>
8
In OWL Lite and OWL DL. In OWL Full they are equivalent.
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