A Prototype Constraint Deductive Database System based on HH¬(C)

This paper presents, from a user point of view, a deductive database system based on Hereditary Harrop Formulas with Constraints and Negation, HH¬(C). The Prolog implementation of this system is based on a fixpoint semantics proposed in a previous work. The answer to a query posed to a database is intended as a constraint of the constraint system associated to C. We have developed several solvers for specific constraint domains, composed of data values and predefined functions and operators, including finite domains, real numbers, Boolean and user-defined enumerated types. They have been implemented by taking advantage of the underlying constraint solvers in SWI-Prolog. In the current version of the system, some improvements regarding the efficiency and the user interface have been introduced. In addition, we have included aggregate functions as count, sum, avg and min. We propose to use aggregate functions as components of the constraint language, so that solving of constraints including aggregate functions is delegated to the constraint solver.