Semantic Query Optimization for Bottom-Up Evaluation

Semantic query optimization uses semantic knowledge in databases (represented in the form of integrity constraints) to rewrite queries and logic programs to achieve eecient query evaluation. Much work has been done to develop various techniques for optimization. Most of it, however, is applicable to top-down query evaluation strategies. Moreover, little attention has been paid to the cost of the optimization. We address the issue of semantic query optimization for bottom-up query evaluation strategies with an emphasis on overall eeciency. We focus on a single optimization technique, join elimination. We discuss factors that innuence the cost of semantic optimization, and present two diierent abstract algorithms for optimization. The rst pre-processes a query statically before it is evaluated ; the second combines query evaluation with semantic optimization using heuristics to achieve the largest possible savings.