A semantics-driven query optimizer for OODBs

Abstract

Semantic query optimization uses problem-specic knowledge (e.g. integrity constraints) for transforming a query into an equivalentone (i.e., with the same answer set) that may be answered more eciently. The optimizer is applicable to the class conjunctive queries is based on two fundamental ingredients. The first one is the ODL description logics proposed as a common formalism to express: class descriptions, a relevant set of integrity constraintsrules (IC rules), queries as ODL types. The second one are DLs (Description Logics) inference techniques exploited to evaluate the logical implications expressed by IC rules and thus to produce the semantic expansion of a given query. The optimizer tentatively applies all the possible transformations and delays the choice of ben-ecial transformation till the end. Some preliminar ideas on ltering activities on the semantically expanded queryare reported. A prototype semantic queryoptimizer (ODB-QOptimizer) for object-oriented database systems (OODBs) is described.