“…In keyword-based search, the user specifies some keywords, and a search engine (e.g., Yahoo, Excite, Alta Vista, and Google) finds those Web pages that contain the keywords, and ranks them according to various measures. In Web information extraction [e.g., 2,13,9,15,8], a wrapper or a specific extraction procedure is built automatically or manually for a Web page to extract some specific pieces of information requested by the user, e.g., extracting the prices of some products. User preference based approaches are commonly used in push type of systems [e.g., 26], where the user specifies what categories of information are interesting to him/her.…”