1. A method for performing a knowledge based web search using a keyword graph, the method comprising: receiving a search request from a user; conducting a web search in response to the search request; determining related terms based on results obtained from the web search; assigning weights onto a keyword graph based on the related terms; determining main nodes of the weighted keyword graph based on modified keyword graph; and identifying relevant main topics from the main nodes of the keyword graph; generating search results based on the relevant main topics.