Technical Report No. 114 - Abstract

Wolfgang May, Paul-Thomas Kandzia
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 forward-chaining construction of a Herbrand-style representation 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. From the F-Logic point of view, the main contribution of the report is to investigate the relationship between inheritance-canonic models as defined in [Kifer-Lausen-Wu-JACM-95] and classical AI frameworks: we show that the semantics which is defined and implemented for F-Logic coincides with the standard semantics of Default Logic and Inheritance Networks. In this report, we restrict ourselves to scalar methods.