35. The method of claim 30 , wherein the set of candidate queries comprises a certain query, and wherein determining costs comprises: determining a partial cost for a first portion of the certain query; and if the partial cost satisfies the first particular mathematical relationship with the current-best cost, determining a second cost based on the entire certain query.
35. The method of claim 30 , wherein the set of candidate queries comprises a certain query, and wherein determining costs comprises: determining a partial cost for a first portion of the certain query; and if the partial cost satisfies the first particular mathematical relationship with the current-best cost, determining a second cost based on the entire certain query. 37. The method of claim 35 , wherein choosing the particular query comprises, if the second cost does not satisfy a second particular mathematical relationship with the current-best cost, then choosing as the particular query a candidate query other than the certain query.