Metadata and the Semantic Web - Web Standards: Mastering HTML5, CSS3, and XML - page 265

Listing 7-69. A Simple RDFS Example
<?xml version="1.0"?>
<rdf:RDF 
xmlns:rdf=" http://www.w3.org/1999/02/22-rdf-syntax-ns# " 
xmlns:rdfs=" http://www.w3.org/2000/01/rdf-schema# " 
xml:base="http://www.example.com/birds#">
<rdf:Description rdf:ID="bird">
<rdf:type rdf:resource=" http://www.w3.org/2000/01/rdf-schema#Class "/>
</rdf:Description>
<rdf:Description rdf:ID="macaw">
<rdf:type rdf:resource=" http://www.w3.org/2000/01/rdf-schema#Class "/>
<rdfs:subClassOf rdf:resource="#bird"/>
</rdf:Description>
</rdf:RDF>
This notation can also be shortened by using rdfs:Class instead of rdf:Description and omitting rdf:type
(Listing 7-70).
Listing 7-70. An Optimized Version of the Previous Example
<?xml version="1.0"?>
<rdf:RDF 
xmlns:rdf=" http://www.w3.org/1999/02/22-rdf-syntax-ns# " 
xmlns:rdfs=" http://www.w3.org/2000/01/rdf-schema# " 
xml:base="http://www.example.com/birds#">
<rdfs:Class rdf:ID="bird" />
<rdfs:Class rdf:ID="macaw">
<rdfs:subClassOf rdf:resource="#bird"/>
</rdfs:Class>
</rdf:RDF>
Web Ontology Language (OWL)
Web Ontology Language is a knowledge representation language with the primary purpose of creating web ontologies .
Web ontologies can be used for a variety of purposes, such as searching, query formation, indexing, and agent or
service metadata management, or to improve application and database interoperability. Web ontologies are especially
useful for knowledge-intensive applications, where text extraction, decision support, or resource planning are
common tasks, as well as in knowledge repositories used for knowledge acquisition.
The abbreviation of the Web Ontology Language, OWL, is not straightforward on purpose [145]. OWL ontologies
are RDF graphs, in other words, sets of RDF triples. Similar to RDF graphs, OWL ontology graphs can be expressed
in various syntactic notations. There are three variants of OWL: OWL Lite , OWL DL , and OWL Full [146]. OWL is a
higher-level language than RDF; in fact, it is a vocabulary extension of RDF. Consequently, RDF graphs are OWL Full
ontologies.
The default OWL namespace is http://www.w3.org/2002/07/owl# , which defines the OWL vocabulary. There is
no MIME type defined specifically for OWL. Using the application/rdf+xml or the application/xml MIME type for
OWL documents is recommended. The recommended file extension is either .rdf or .owl .
The development of the first version of OWL was started in 2002, and the second version, OWL2, in 2008. OWL
became a W3C Recommendation in 2004 [147], and OWL2 was standardized in 2009 [148, 149].