The Semantic Web - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 30

< rdf:RDF xmlns:rdf=”http://www.w3.org/1999/02/22 − rdf − syntax − ns#”
xmlns:ex=”http://example.org/#”
xml:base=”http://example.org/” >
< rdf:Description about=”#john” >
< ex:hasName rdf:parseType=”Resource” >
< ex:firstName > John < /ex:firstName >
< ex:lastName > Smith < /ex:lastName >
< /ex:hasName >
< /rdf:Description >
< /rdf:RDF >
Fig. 3.4. Example RDF/XML serialization
3.2.1 RDF Schema
RDF Schema (RDFS) is a lightweight ontology language for defining vocab-
ularies for RDF. Unlike XML Schema, which prescribes the order and com-
binations of tags (the structure) in an XML document, RDF Schema only
provides information about the interpretation of the statements given in an
RDF data model. RDF Schema does not say anything about the syntactical
appearance of the RDF description. RDFS can in fact be seen as an extension
of RDF with a vocabulary for defining classes, class hierarchies, properties (bi-
nary relations), property hierarchies, and property restrictions. RDFS classes
and properties can be instantiated in RDF. For a more detailed comparison of
XML Schema and RDF Schema we refer the reader to [74]. Figure 3.5 shows
the graph which corresponds to the is-a hierarchy of Fig. 3.2.
Fig. 3.5. RDFS ontology of persons and working group members
RDF(S) (referring to the combination of RDF and RDF Schema) is not
very expressive compared with many other ontology languages, as it allows
only the representation of concepts, concept taxonomies, and binary relations.
The expressive limitations of RDF(S) were a major motivation for developing
more expressive languages for the Semantic Web. In the remainder of this
chapter, we describe the ontology and rules components which are layered on
top of RDF(S).