Reasoning About Persistence: A Theory of Actions

Abstract

Winslett proposed a method for reasoning about action called the possible models approach (PMA). The PMA successfully removed the major difficulty manifested by Ginsberg and Smith's possible worlds approach (PWA). In this paper, we show that Winslett's PMA fails to solve the frame and ramification problems for some actions, as does the PWA. From this observation, we classify actions as definite and indefinite, and find that, in general, the PMA is not appropriate for both definite and indefinite actions. We propose a new approach to formalize actions based on persistence. We compare our approach with the PMA in detail, and show that our new formalization can avoid the problems in the PMA and PWA in most cases, and give more intuitive results for reasoning about action, regardless of whether the action is definite or indefinite.