For this purpose, a number of quality rating methods for Web pages (Amento et al., 2000;Zhu and Gauch, 2000) can be used.
since Google (i.e., the search engine used in our system) rates the quality of pages based on hyperlink information, and selectively retrieves those with higher quality (Brin and Page, 1998), we tentatively regarded P Q (d) as a constant.