1. A method comprising: under control of one or more processors configured with executable instructions, receiving crawled web pages corresponding to a plurality of uniform resource locators (URLs) provided to a web crawler; sorting the crawled web pages into a plurality of labeled groups based at least in part on user behavior information reflecting behavior of users with respect to at least some of the crawled web pages; and establishing one or more hierarchical relationships between the plurality of labeled groups based at least in part on a determined relative priority of each labeled group for inclusion in an index, the one or more hierarchical relationships between the plurality of labeled groups including at least one hierarchical relationship between a first labeled group of the plurality of labeled groups and a second labeled group of the plurality of labeled groups.