14. The medium of claim 12 , wherein the operations comprise: determining that the score assigned to the one or more query term optionalization rules that are specific to the particular query term does not satisfy a threshold; and removing the one or more query term optionalization rules that are specific to the particular query term from a set of query term optionalization rules that includes other query term optionalization rules that are specific to other query terms, the other query term optionalization rules indicating whether the other query terms should be made optional in revisions of search queries that include the other query terms, based on determining that the score assigned to the one or more query term optionalization rules that are specific to the particular query term does not satisfy the threshold.
12. The medium of claim 11 , wherein the operations comprise assigning a score to the one or more query term optionalization rules that are specific to the particular query term based at least on the click count and the skip count.