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Listing 7-51.
Dublin Core in RDF/XML
<?xml version="1.0"?>
<!DOCTYPE rdf:RDF PUBLIC "-//DUBLIN CORE//DCMES DTD 2002/07/31//EN"
<rdf:RDF xmlns:rdf="
http://www.w3.org/1999/02/22-rdf-syntax-ns#
"
xmlns:dc="
http://purl.org/dc/elements/1.1/
"
>
<rdf:Description>
<dc:title>Internet for everyone</dc:title>
<dc:creator>Leslie Sikos</dc:creator>
<dc:format>Book</dc:format>
<dc:identifier>ISBN 963 9425 08 7</dc:identifier>
</rdf:Description>
</rdf:RDF>
XML character-encoding rules apply. Optionally, the language of any element in these documents can be
provided by the
xml:lang
attribute.
Expressing Qualified Dublin Core in RDF is described by another DCMI specification [117]. In contrast,
properties such as
dc:creator
and
dc:date
are considered in this document as entities rather than names.
Listing 7-52 shows an example.
Listing 7-52.
Qualified Dublin Core in RDF
<http://www.example.com> dc:creator <http://www.example.org/pj>
The original specifications defining the RDF implementations of DC have been superseded by the 2008
specification [118] and notes [119]. For example, the RDF schemas for DCMI properties and classes have been
removed from the specification.
Knowledge Representation Standards
Resource Description Framework (RDF)
Although it was originally designed as a metadata data model,
Resource Description Framework
(
RDF
) has become a
general web resource description and modeling language. It can be used for conceptual description or modeling of
information stored in web resources. RDF can be used to create a machine-readable description about any kind of
resource, because RDF files can be extended with an arbitrary number of external vocabularies. In contrast to many
W3C standards, RDF has no single specification but is defined by a set of documents [120].
The RDF data model can be used for describing any kind of resources that can be identified by a URI. As
mentioned earlier, an RDF document is a sequence of statements called
RDF
triples
(resource-property-value or
subject-predicate-object). The predicate (property) that denotes a relationship between the subject and the object
can be binary only. Any expression in RDF is a collection of triples. A set of triples is called an
RDF graph
, which is a
directed, labeled graph that represents information on the Web. The nodes of the RDF graph are the resources and
values [121].
As shown earlier, a person can be described using the FOAF vocabulary. Such descriptions can be written either
in XML or in RDF. Listing 7-53 shows how to write FOAF in RDF.
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