International Publisher for Advanced Scientific Journals (IPASJ)
Search engines play an important role in information retrieval on the web. Given a query, search engines, such as Google, Yahoo! and Bing, return a ranked list of results. For different queries, the result set includes documents on a variety of topics, rather than a single topic. This variation is probably due to the matter that a typical query contains about only two to three terms, which is not sufficient to locate the desired information unambiguously.