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 labeled groups based at least in part on a determined relative priority of each labeled group for inclusion in an index.