A search engine comprising a crawler which crawls the WWW and stores pages found on the WWW in a database. An indexer indexes the pages in the database to produce a primary index. A document mapping section maps pages in the database into a plurality of tiers based on a ranking of the pages. The ranking...http://www.google.fr/patents/US7240064?utm_source=gb-gplus-shareBrevet US7240064 - Search engine with hierarchically stored indices
