Semantic Web
A real-world implementation of semantic analysis is the Semantic Web (www.w3.org/2001/sw). The Semantic Web, sometimes referred to as "Web 3.0," introduces interpretive analysis to the vast amounts of information available over the World Wide Web. In achieving this goal, authors must augment existing data in a formal way that lets machines interpret the information unambiguously. For example, the meaning of "hand" is context sensitive. Therefore, ontology must somehow account for the different ways in which the word may be used. The Semantic Web as proposed by W3C provides two mechanisms to handle semantic information and ontology creation: Resource Definition Framework (RDF) and Web Ontology Language (OWL).
A Resource Definition Framework (www.w3.org/RDF) is a means to create simple associations between elements. RDF introduces a 3-tuple (triple) to define associations between resources, in a manner similar to sentence structure:
- Subject. A resource as defined by a URI.
- Predicate. Indicates the type of relationship between subject and object.
- Object. The resource that is the terminating end of the relationship.
Put another way, a resource (subject) has a property (predicate) given by another resource (object). There is no constraint on the number of objects associated with a subject. That is to say, a resource can have multiple resources as properties. For example, Listing One uses RDF to define a website with two coauthors. RDF triples can be represented by directed graphs like that in Figure 1.
<?xml version="1.0" encoding="UTF-8" ?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc="http://purl.org/DC/"
xmlns:os="http://somesite.org/Schema/">
<rdf:Description about="http://rama.cpe.fr/index.html">
<dc:Creator rdf:resource="mailto:[email protected]"/>
<dc:Title> Index of my web site </dc:Title>
<dc:Creator>
<rdf:Description about="mailto:[email protected]">
<os:worksWith rdf:resource="mailto:[email protected]"/>
</rdf:Description>
</dc:Creator>
</rdf:Description>
</rdf:RDF>[http://bat710.univ-lyon1.fr/~champin/rdf-tutorial/node23.htmlBC1]
The Web Ontology Language (www.w3.org/TR/owl-features) is a formal language for specifying resources and their relationships. OWL is built on top of RDF, and supports a number of mathematical relations among resources.
OWL has several versions. OWL Full is an extension of RDF to provide a formal ontology language. OWL Descriptive Logic (OWL DL) supports semantics expressible as First Order Logic. OWL Lite is a version of OWL DL constructed for ease of implementation.
