Abstract

Abstract. Obligation change raises the "frame problem " which is to characterise what obligations remain unchanged after an action has been performed. Many general solutions have been proposed but even if they are attractive from a thoretical point of view they have practical drawbacks. In this paper simple solutions are proposed thanks to the restriction to obligations that take the form of modal literals. These solutions are presented in the framework of dependence logic and of situation calculus, and it is shown that they are based on the same intuitive idea. This idea is to express that we have a complete representation of actions and circumstances that can change an obligation. 1 Introduction The problem of the characterisation of what remains to be true after the per-formance of an action is recognised as a difficult problem in the field of Articial Intelligence. This problem is usually called the "frame problem".The same problem arises in the field of deontic logic if we want to characterise the set of obligations that persist after an action. It has some connections withdeontic defeasibility but it is not the same problem (see [10, 1, 12, 9, 17]). An interesting solution to the frame problem has been proposed by Reiter [11]in the framework of situation calculus for modelling the evolution of the world. Later on this solution has been extended to the evolution of beliefs about theworld by Scherl and Levesque [16, 14]. This work has been extended to revision by Shapiro et al. in [15]. In [4] Demolombe has adapted their intuitive ideasto the evolution of obligations. However, this solution has practical drawbacks because it requires to assign to all the ideal situations an ideality level in thesame way as Scherl and Levesque require the assignement of a plausibility level.

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