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Semantic Web

The Semantic Web is a vision of the future of the World Wide Web proposed by Tim Berners-Lee consisting of documents that are put together in such a way that it facilitates automated information gathering and research in a far more meaningful way than can be accomplished with current web search tools.

The usability and usefulness of the Web and its interconnected resources will be enhanced through:

documents 'marked up' with semantic information (an extension of the <meta> tags used in today's Web pages to supply information for Web search engines using web crawlers). This could be machine-readable information about the human-readable content of the document (such as the creator, title, description, etc of the document) or it could be purely metadata representing a set of facts (such as resources and services elsewhere in the site).
(Note that anything that can be identified with a Universal Resource Identifier (URI) can be described, so the semantic web can reason about people, places, ideas, cats etc.)
common metadata vocabularies (ontologies) and maps between vocabularies that allow document creators to know how to mark up their documents so that agents[?] can use the information in the supplied metadata (so that Author in the sense of 'the Author of the page' won't be confused with Author in the sense of a book that is the subject of a book review).
automated agents to perform tasks for users of the Semantic Web using this metadata
web-based services (often with agents of their own) to supply information specifically to agents (for example, a Trust service that an agent could ask if some online store has a history of poor service or spamming).

The primary facilitators of this technology are: URIs (which identify resources) along with XML and Namespaces. These, together with a bit of logic form RDF, which can be used to say anything about anything. As well as RDF, many other technologies such as Topic Maps and pre-web AI technologies are likely to contribute to the Semantic Web.

All current web technologies are likely to have a role in the semantic web (in the sense of semantic world wide web), for instance :

DOM The Document Object Model which provides a set of standard interfaces for accessing XML and HTML document components.
XPath, Xlink[?], XPointer
XInclude[?] XML fragment[?] XML query language XHTML
RDF (Resource Description Framework)
XSL, XSLT Extensible Stylesheet Language
SVG (Scalable Vector Graphic)
SMIL
SOAP
DTD
the concept of metadata.

You can create a piece of RDF code to describe yourself to the Semantic Web using the Friend-of-a-Friend-o-matic (http://www.ldodds.com/foaf/foaf-a-matic)