Semantic simply means “meaning”. 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. In today’s web, most web pages add basic semantics for search engines using the tag; however, they are merely isolated keywords and lack linkages to provide a more meaningful context. These semantics are weak and limit searches to exact matches.
Semantics give a keyword symbol useful meaning through the establishment of relationships. (For example, a standalone keyword such as building exists on a web page. The tag surrounds the building keyword to indicate its importance. However, if the keyword relates to other keywords in defined relationships, a web of data or context forms, that reveals semantics. So building relates to various other keywords such as architect, building plans, construction site, and so on-the relationships expose semantics.
Thus the Semantic Web is simply a web of data described and linked in ways to establish context or semantics that adhere to defined grammar and language constructs.
The WWW consists primarily of content for human consumption. Content links to other content on the WWW via the Universal Resource Locator (URL). The URL relies on surrounding context (if any) to communicate the purpose of the link that it represents; usually the user infers the semantics. Web content typically contains formatting instructions for a nice presentation, again for human consumption. WWW content does not have any formal logical constructs. Correspondingly, the Semantic Web consists primarily of statements for application consumption. The statements link together via constructs that can form semantics, the meaning of the link. Thus, link semantics provide a defined meaningful path rather than a user-interpreted one. The statements may also contain logic that allows further interpretation and inference of the statements.
The Semantic Web is solidly grounded on graph theory and description logic. Statements and corresponding relationships establish both concepts (e.g., a Person has a birth date) and instances (e.g., John is a friend of Bill). Statements that define concepts and their relationships form ontology. Statements that refer to individuals form instance data. Statements can be asserted or inferred. The former requires the application to create the statement directly, to assert the statement. The latter requires a reasoner to infer additional statements logically. (That John is an associate of Bill is inferred from the asserted statements.) The Semantic Web offers several languages. Rather than have one language fit all information and programming needs, the Semantic Web offers a range from basic to complex. This provides Semantic Web applications with choices to balance their needs for performance, integration, and expressiveness. A set of statements that contribute to the Semantic Web exists primarily in two forms; knowledge bases and files. Knowledge base offer dynamic, extensible storage similar to relational databases. Files typically contain static statements.