Nowadays, Internet goes deep into human beings' daily routines and brings us many remarkable conflicts between mass digital information and our limited capabilities of acquiring them. Search engine thus becomes an important channel of obtaining information. But conventional search engines can index less than 16% of the publicly indexable Webs, and the other 84% are "invisible". Moreover, the public information on the Invisible Web is 400-550 times larger than WWW. Thus users are searching only 0.03% of available pages. Therefore, it's urgent to seek efficient methods to solve the retrieval pro...
