Search engines are one tool used to answer information needs. Search engines are huge databases of web pages as well as software packages for indexing and retrieving the pages that enable users to find information of interest to them. The search engines directories, portals and indexes are the web’s “Catalogues” allowing a user to carry out the task of searching the web for information that he/she requires. Users express their information needs as queries. Usually informally expressed as two or three words (we call this a ranked query). Web-Search
Around 48.4% of users submit just one query in a session, 20.8% submit two, and about 31% submit three or more. Less than 5% of queries use Boolean operators (AND, OR, and NOT), and around 5% contain quoted phrases. The Web searches the Web-based content.
The web creates new challenges for information retrieval. The amount of information on the web is growing rapidly as well as the number of new users. The search engines that rely on keywords matching usually return too many, low quality matches. To make matter worse and high quality we have to build a large scale search engines which address many of the existing system.