The authors describe a scheme to utilize semantic knowledge in optimizing a user-specified query. The semantics is represented as function-free clauses in predicate logic. The scheme uses a graph-theoretic approach to identify redundant joins and restrictions present in a given query while adding additional profitable specifications to it. Dynamic and heuristic interaction of three entities-schema, semantics, and query-forms the basis of the algorithm. The implementation architecture of the algorithm and test results on a representative set of data are presented. Issues associated with updating of semantic constraints are addressed, and an algorithm for semantic maintenance is introduced.>

This paper describes a scheme to utilize semantic integrity constraints in optimizing a user specified query. The scheme uses a graph theoretic approach to identify redundant join clauses and redundant restriction clauses specified in a user query. An algorithm is suggested to eliminate such redundant joins and avoid unnecessary restrictions. In addition to these eliminations, the algorithm aims to introduce as many restrictions on indexed attributes as possible, thus yielding an equivalent, but potentially more profitable, form of the original query.