The Resource Description Framework - Linked Data: A Geographic Perspective - page 79

“ has _ longitude ,” “ has _ latitude ,” “ has _ name ,” and so on. An ontology
would say that Pub and TopographicObject are classes, that Pub is a subclass
of TopographicObject , and that the class TopographicObject can have the
properties “ has _ longitude ,” “ has _ latitude ,” and “ has _ name. ”
We can state all these things using the RDFS language, that is, which classes we
have and which properties each class is allowed to take. The rules of inheritance
mean that a property of a class will also be a property of its subclass. This makes
sense when thinking about an example: If TopographicObject has the property
“ has _ longitude ,” and a Pub is a kind of TopographicObject , then Pub
can also use the property “ has _ longitude. ” A second rule states that if, for
example, Pub is a kind of TopographicObject , and Freehouse 10 is a kind
of Pub , then Freehouse is also a kind of TopographicObject . This kind
of inference is known as transitivity , so we can say that the rdfs:subClassOf
relationship is transitive.
5.6.3 RDFs s yNTaX : C Lasses aND p RopeRTies
Let us use an example to introduce the syntax of RDFS.
1 <?xml version = “1.0” encoding = “UTF-8”?>
2 <rdf:RDF
3 xmlns:rdf = “ http://www.w3.org/1999/02/22-rdf-syntax-ns#”
4 xmlns:rdfs = “ http://www.w3.org/200/01/rdf-schema#”
5 xmlns:mereaMaps = “ http://mereamaps.gov.me/topo/” >
6
7 <rdf:Description
6 rdf:about = “ http://mereamaps.gov.me/topo/Pub” >
8 <rdf:type
9 rdf:resource = “ http://w3.org/2001/01/rdf-schema#Class”/ >
10 <rdfs:subClassOf rdf:resource = “mereaMaps:TopographicObject”/>
11 </rdf:Description>
12 </rdf:RDF>
The language constructs in RDFS are themselves classes and properties. Any
application that knows the vocabulary will know what classes and properties to
expect and can process the data, including from multiple documents using the same
ontology. The two basic classes within the RDFS language are
• rdfs:Class , which is the class of resources that are RDF classes
• rdf:Property , which is the class of all RDF properties
The example states that Pub is a Class (using the rdf:type property
and rdfs:Class as the object of the triple, lines 8 and 9) and a subclass of
Topographic Object (using the rdfs:subClassOf property, line 10).