Optimization of object-oriented queries through pushing selections

Abstract

We propose a new optimization method for object-oriented queries. The method enables pushing selection conditions before structure constructors, joins and quantifiers. A less general variant of this method is known from relational systems and SQL as pushing a selection before a join. If a query involves a selection which predicates refer to proper arguments of a structure constructor or a join or a quantifier that occurs at the left-hand subquery of this query then it can be rewritten. The rewriting consists in pushing such predicates down before a proper operator. The approach follows the stack-based approach (SBA) and its query language SBQL (Stack-Based Query Language). The assumed strong typing based on the compile time simulation of run-time actions gives the possibility to solve this optimization problem in its full generality. The paper presents examples how the optimization method works. General features of the implemented algorithm are also presented. © 2013 Springer-Verlag.