Data Constructors: On the Integration of Rules and Relations

Abstract

Although the goals and means of rule-based and data-based systems aretoo different to be fully integrated at the present time, it seems appropriate toinvestigate a closer integration of language constructs and a better cooperationof execution models for both kinds of approaches.In this paper, we propose a new language construct called constructor that â€" when applied to a base relation â€" causes relation membership to become truefor all tuples constructable through the predicates provided by the constructordefinition. The approach is shown to provide expressive power at leastequivalent to PROLOG's declarative semantics while blending well both with astrongly typed modular programming language and with a relational calculusquery formalism. A three-step compilation, optimization, and evaluation methodologyfor expressions with constructed relations is described that integratesconstructors with the surrounding database programming environment. In particular,many recursive queries can be evaluated more efficiently within theset-construction framework of database systems than with proof-orientedmethods typical for a rule-based approach.