Query optimization by using knowledge about data semantics

In this paper we address the problem of using semantic properties of data within the process of query optimization. The discussion is in terms of the relational data model. We present query transformation rules, called semantic transformation rules (or simply stemantic rules), that are based on the database properties expressed by the integrity constraints. The semantic rules presented in the paper allow join elimination, clustering index introduction and empty query test according to the content of the integrity constraints. We provide a formal proof of the correction of such transformation rules. We also investigate the problem of using semantic rules within transactions, where any arbitrary sequence of queries and modification operations may occur, and semantic integrity can be violated during intermediate steps of processing. Conditions are provided under which the semantic rules presented in the paper can be correctly applied to transform queries occurring within compiled transactions.