Optimization of object-oriented queries addressing large and small collections

When a query jointly addresses very large and very small collections it may happen that an iteration caused by a query operator is driven by a large collection and in each cycle it evaluates a subquery that depends on an element of a small collection. For each such element the result returned by the subquery is the same. In effect, such a subquery is unnecessarily evaluated many times. The optimization rewrites such a query to reverse the situation: the loop is to be performed on a small collection and inside each its cycle a subquery addressing a large collection is evaluated. We illustrate the method on comprehensive examples and then present the general rewriting rule. The research follows the Stack-Based Approach to query languages having roots in the semantics of programming languages. The optimization method consists in analyzing of scoping and binding rules for names occurring in queries.