A New Optimization Algorithm for Queries with Expensive Selections

In this paper,one of the new problems encountered in the query optimization of ORDB(object relational data base),that is,how to optimize the expensive predicates contained in the query,is discussed.In traditional query optimizers,selections have been handled by “pushdown” rules under the assumption that selection can be processed with little time or no time,and selections are processed immediately after the scan of the relation,so as to diminish the size of relations to be joined.In ORDB,however,complex methods can be embedded in selections,thus selections may take significant amount of time,and the assumption for “pushdown” is no longer sound,so attention must be paid on this new problem.Based on the analysis of some solutions,a new algorithm Predicate _Rolling _Up is presented.