Nonmonotonic Inheritance in Object-Oriented Deductive Database Languages

Deductive object-oriented frameworks integrate logic rules and inheritance. There, specific problems arise: Due to the combination of deduction and inheritance, (a) deduction can take place depending on inherited facts, thus raising indirect conflicts, and (b) also the class hierarchy and-membership is subject to deduction. From this point of view, we investigate the application of the extension semantics of Default Logic to deductive object-oriented database languages. By restricting the problem to Horn programs and a special type of defaults tailored to the semantics of inheritance, a forwardchaining construction of extensions is possible. This construction is compared with a solution as implemented in the F-Logic system Florid which is based on a combination of classical deductive fixpoints and an inheritance-trigger mechanism. The paper is a condensed version of [MK98]