Information Technology Reference
In-Depth Information
3
The Semantic Web
A major drawback of XML is that XML documents do not convey the mean-
ing of the data contained in the document. Exchange of XML documents over
the Web is only possible if the parties participating in the exchange agree be-
forehand on the exact syntactical format (expressed in XML Schema) of the
data. The Semantic Web [13] allows the representation and exchange of infor-
mation in a meaningful way, facilitating automated processing of descriptions
on the Web.
Annotations on the Semantic Web express links between information re-
sources on the Web and connect information resources to formal terminologies
- these connective structures are called ontologies. Ontologies [38] form the
backbone of the Semantic Web; they allow machine understanding of infor-
mation through the links between the information resources and the terms
in the ontologies. Furthermore, ontologies facilitate interoperation between
information resources through links to the same ontology or links between
ontologies.
The term “ontology” originates from philosophy and has been adopted in
the field of Computer Science with a slightly different meaning [53]:
An ontology is a formal explicit specification of a shared conceptualization.
In the late 1990s the idea of a Semantic Web [13] boosted interest in the
development of ontologies even further. The general conviction held by the
W3C is that the Semantic Web needs an ontology language that is compatible
with current Web standards and is in fact layered on top of them. The language
needs to be expressed in XML and, preferably, should be layered on top of
RDF(S) (an overview of these languages is provided later in this chapter).
An often used depiction of the vision of Semantic Web languages is the
“Semantic Web layer cake.” The original layer cake
1
, which featured a rules
language layered on top of the ontology language, was presented at XML2000
by Tim Berners-Lee, director of the World Wide Web Consortium (W3C). It
1
http://www.w3.org/2000/Talks/1206-xml2k-tbl/slide10-0.html
.
Search WWH ::
Custom Search