7. The method of claim 6 , wherein the first tags include first prefixes and first suffixes that appear in the first query with the first phrases, and the second tags include second prefixes and second suffixes that appear in the second query with the second phrases.
6. The method of claim 1 , wherein measuring the click similarity includes determining numbers of clicks by the users on individual URLs in: the first set of URLs, the second set of URLs, and shared URLs that appear in both the first set and the second set.