Towards Generalized Rule-based Updates

Abstract

Recent work on rule-based updat es provided new frameworks for updates in more general knowledge domains [Marek and Truszczriski , 1994; Baral, 1994; Przymusinski and Turner , 1995]. In this paper , we consider a simple generalization of rule-based updates where incomplete knowledge bases are allowed and updat e rules may contain two types of negations. It turns out that previous methods cannot deal with this generalized rule-based update properly. To overcome the difficulty, we argue that necessary preferences between update rules and inertia rules must be taken into account in update specifications. From this motivation , we propose prioritized logic programs (PLPs) by adding preferences into extended logic programs [Gelfond and Lifschitz , 1991] . Formal semantics of PLPs is provided in terms of the answer set semantics of extended logic programs. We then show that the procedure of generalized rule-based update can be formalized in the framework of PLPs. The minimal change property of the update is also investigated.