17. 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: obtaining first search results that were generated for a search query; determining, by operation of a system, a first search results score associated with the first search results, wherein the first search results score is based on (i) a respective rank of each first search result, and (ii) a respective first popularity score associated with each first search result; revising the search query using a query revision rule; obtaining second search results that were generated for the revised search query; determining a second search results score associated with the second search results, wherein the second search results score is based on (i) a respective rank of each second search result, and (ii) a respective second popularity score associated with each second search result; determining that a difference between the first search results score and the second search results score satisfies a specified threshold; and in response to determining that a difference between the first search results score and the second search results score satisfies the specified threshold, identifying the query revision rule as a good revision rule for the search query.
17. 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: obtaining first search results that were generated for a search query; determining, by operation of a system, a first search results score associated with the first search results, wherein the first search results score is based on (i) a respective rank of each first search result, and (ii) a respective first popularity score associated with each first search result; revising the search query using a query revision rule; obtaining second search results that were generated for the revised search query; determining a second search results score associated with the second search results, wherein the second search results score is based on (i) a respective rank of each second search result, and (ii) a respective second popularity score associated with each second search result; determining that a difference between the first search results score and the second search results score satisfies a specified threshold; and in response to determining that a difference between the first search results score and the second search results score satisfies the specified threshold, identifying the query revision rule as a good revision rule for the search query. 24. The system of claim 17 , further comprising: storing the query revision rule for use in revising the search query.