Contextual logic of change and the ramification problem

Abstract

In this paper we discuss CLOG, an approach for reasoning about action and change, which is an alternative to the situation calculus and circumscription. In our approach, inspired by the possible worlds approach, change is modeled as changing the theory that describes the world. CLOC extends first order logic by representing changes, defining predicates about the execution of change and defining new inference rules that handle change. We also present a rule of inference, EX _Pμ, that is used for concluding what propositions hold after the execution of change. We study the ramification problem and conclude that our approach presents the correct solution for the example Baker uses to show that his approach doesn't solve the ramification problem. We also show that our method is highly sensitive to the choice of formulation used to describe the situations involved, since some variations would be enough to make our method suffer from the ramification problem. We conclude that this is a problem of choosing adequate formulation of both situations and actions. We identify the conditions under which our method solves this problem and make suggestions for avoiding it.

We thank Prof. Carlos Pinto Ferreira, the anonymous reviewers and the members of GIA for their for their helpful comments. This work was partially supported by Junta Nacional de Investigação Científica e Tecnológica and by PRAXIS XXI under grant 2/2.1/TIT/1568/95.