**3. Knowledge and Semantic web**

The growth of the World Wide Web has been tremendous since its evolvement both in terms of the content and the technology. The first Web generation was mainly presentation based. They provided information through the Web pages but did not allow users to interact with them. In short, they contained read only information. Moreover, they were only text pages and do not contain multimedia data. These Web sites have higher dependency on the presentation languages like Hypertext Markup Languages (HTML) (Horrocks, et al., 2004). With the introduction of e**X**tensible**M**arkup**L**anguage (XML), the information within the pages became more structured. Those XML based pages could hold up the contents in more structured method but still lack the proper definition of semantics within the contents, (Berners-Lee, 1998). For this reason, the needs of intelligent systems which could exploit the wide range of information available within the Web are widely felt. Semantic Web is envisaged to address this need.

The term "*Semantic Web*" is coined by Tim Berners-Lee in his work (Lee, et al., 2001) to propose the inclusion of semantic for better enabling machine-people cooperation for handling the huge information that exists in the Web. The term "*Semantic Web*" has been defined numerous time. Though there is no formal definition of Semantic Web, some of its most used definitions are "*The Semantic Web is not a separate Web but an extension of the current one, in which information is given well-defined meaning, better enabling computers and people to work in cooperation. It is a source to retrieve information from the Web (using the Web spiders from RDF files) and access the data through Semantic Web Agents or Semantic Web Services. Simply Semantic Web is data about data or metadata*" (Lee, et al., 2001). "*A Semantic Web is a Web where the focus is placed on the meaning of words, rather than on the words themselves: information becomes knowledge after semantic analysis is performed. For this reason, a Semantic Web is a network of knowledge compared with what we have today that can be defined as a network of information*" (Huynh, et al., 2007). "*The Semantic Web provides a common framework that allows data to be shared and reused across application, enterprise and community boundaries*" (Decker, et al., 2000). In the next subsection, we discuss the different issues related to the definition of such a technology where we focus mainly on the Description Logic theory (DL) and its impact on the semantic web technology.
