What is the Semantic Web?

The World Wide Web has emerged as an important part of our everyday lives in the last decade. People use the web to share information; companies use it to advertise their products; government organizations use it to make everyday submission of taxes and bill easier; people use e-groups to facilitate information exchange within their community and educational institutions use the web to deliver teaching material and online training.
This has resulted in widespread popularity of the web and as a result, the number of pages available in the global information space has grown exponentially. This makes it extremely difficult for users to locate and access information that they require. When one needs to search the Web for some specific information, it results in a large number of hits in the form of search results that have to be scanned and filtered manually to get at the desired information. The number of matches is so large that the specific information required may even be missed.
Since the meaning, i.e. - the semantics of the information is not understood by machines, it is difficult for machines to extract information of relevance for human use from weakly structured HTML documents. Besides this, data can be shared between applications only via cut and paste because the way in which data is stored in web pages, the semantics of the data is lost; the web pages do not carry any semantic information along with the data.
Therefore, in recent years, the awareness to these problems has resulted in a need for information in the web to be structured in such a way that the semantics of the data be accessible to machines. The information must be semantically annotated so that software agents and desktop applications can directly access and process it. In other words, the current web needs to be augmented so that the semantics of the Web pages is machine-process able.
Tim Berners-Lee the originator of the Web sees the Semantic Web as an extension of the current web in which information is given well defined meaning, better enabling computers and people to work in cooperation. The meaning of the information on a Web page is formalized using semantic meta-data that is based on concepts defined in ontologies.
The Semantic Web is the future of the World Wide Web. It is a cooperative effort to build an architecture for the World Wide Web by formatting the content in terms of metadata so that it can be understood by a software agent. The web as it stands now contains vast amounts of information, all of which has been structured for human consumption. The idea behind the semantic web is to provide structure to this information so that it can be read and interpreted by a computer. An agent can visit a page which has been extended with metadata and understand the kind of data contained in that page and then use it to make inferences or decisions about what to do with that data. It enables the agent to respond to unforeseen situations.
Users often want to use the Web to do more than just locate a document, they want to perform some task. For example, a user might want to find the best price on a desktop computer, plan and book a family vacation to a distant city, or make reservations at a moderately-priced Indian restaurant within five kilometers of the movie they plan to see that evening. Completing these tasks often involves visiting a series of pages, integrating their content and reasoning about them in some way. This is far beyond the capabilities of contemporary directories and search engines.
The main obstacle is the fact that the Web was not designed to be processed by machines. Although, web pages include special information that tells a computer how to display a particular piece of text or where to go when a link is clicked, they do not provide any information that helps the machine to determine what the text means. Thus, to process a web page intelligently, a computer must understand the text, but natural language understanding is known to be an extremely difficult and unsolved problem. Some researchers and web developers have proposed that we augment the Web with languages that make the meaning of web pages explicit. Tim Berners-Lee, inventor of the Web, has coined the term Semantic Web to describe this approach. 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.