15. The system of claim 9 , wherein the query term proximity rule comprises a query term revision rule for revising search queries by separating the particular query term and the one or more other query terms by a particular number of words.
9. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: accessing query log data that identifies, for a search query: a particular query term and one or more other query terms that are included in the search query, search results that were generated using the search query, a ranking of the search results that were generated using the search query, and a particular search result selected by a user from among the search results that were generated using the search query; determining, using the query log data, that, (i) in text associated with the particular search result selected by the user, the particular query term is separated from all of the one or more other query terms by at least a predetermined minimum number of terms, and (ii) in text associated with a search result that was ranked higher than the particular search result selected by the user, the particular query term is not separated from all of the one or more other query terms by at least the predetermined minimum number of terms; and based on the determination, incrementing a click count for a query term proximity rule corresponding to the particular query term.