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.