Design and Implementation of a Three-Step Intensional Query Processing Scheme

When processing a query in a conventional database, a set of facts (extensional answers) are usually returned for an answer set. This can be different in a deductive or expert database system. Users may, as before, be interested in a set of facts to answer their query, but in certain queries users are also able to get the answer of a query as a set of formulas (intensional answers). These “intensional answers†can greatly reduce the costs of processing a query, can be represented in a more compact way than a large set of facts, and are moreover independent of the current state of the database. In this paper, we introduce an intensional query processing technique composed of three steps and its implementation in Prolog. The three steps are pre-resolution, resolution, and post-resolution. In pre-resolution step, deductive rules are transformed into certain forms. In resolution step, SLDresolution is applied until the last resolvents consist of either extensional literals or comparison literals. In post-resolution step, intensional answers are generated and checked against integrity constraints to remove meaningless answers. Our work is an extension to Cholvy and Demolombe (1986), and Pascual and Cholvy (1988).