18. The method of claim 15 , wherein determining the set of candidate queries and costs comprises: initially establishing the query as a current-best query; determining a current-best cost based on the current-best query; for each certain query of the set of candidate queries: determining a current cost based on the certain query; if the current cost satisfies a first particular mathematical relationship with the current-best cost, then: establishing the certain query as the current-best query; and establishing the current cost as the current-best cost.
18. The method of claim 15 , wherein determining the set of candidate queries and costs comprises: initially establishing the query as a current-best query; determining a current-best cost based on the current-best query; for each certain query of the set of candidate queries: determining a current cost based on the certain query; if the current cost satisfies a first particular mathematical relationship with the current-best cost, then: establishing the certain query as the current-best query; and establishing the current cost as the current-best cost. 23. The method of claim 18 , wherein the first particular mathematical relationship is “less than”.