EXTERNAL SEMANTIC QUERY SIMPLIFICATION: A GRAPH-THEORETIC APPROACH AND ITS IMPLEMENTATION IN PROLOG

Abstract

Semantic query simplification utilizes integrity constraints enforced in a database system for reducing the number of tuple variables and terms in a relational calculus query. To a large degree, this can be done by a system that is external to the DBMS. The paper advocates the application of database theory in such a system and describes a working prototype of an external semantic query simplifier implemented in Prolog. The system employs a graph-theoretic approach to integrate tableau techniques and algorithms for the syntactic simplification of queries containing inequality conditions. The use of integrity constraints is shown not only to improve efficiency but also to permit more meaningful error messages to be generated, particularly in the case of an empty query result. The paper concludes with outlining an extension to the multi-user case.