6. The method of claim 5 , further comprising: determining whether the low execution plan equals the current execution plan; and determining whether the high execution plan equals the current execution plan.
6. The method of claim 5 , further comprising: determining whether the low execution plan equals the current execution plan; and determining whether the high execution plan equals the current execution plan. 7. The method of claim 6 , further comprising: if a low execution plan and a high execution plan equal the current execution plan, then terminating execution of the expressions in the subset of the set of relevant expressions; and defining the current execution plan as the cardinality-optimal query execution plan.