Journal of Artificial Intelligence Research 30 (2007) 361-412 Submitted 07/07; published 11/07 Natural Events John Bell
[email protected] Department of Computer Science, Queen Mary, University of London, London E1 4NS, UK Abstract This paper develops an inductive theory of predictive common sense reasoning. The theory provides the basis for an integrated solution to the three traditional problems of reasoning about change; the frame, qualification, and ramification problems. The theory is also capable of representing non-deterministic events, and it provides a means for stating defeasible preferences over the outcomes of conflicting simultaneous events. 1. Introduction A great deal has been written on the logical representation of common sense reasoning about change since the publication of McCarthy and Hayes’s (1969) seminal paper, and many theories have been proposed; see, for example, the monographs by Sandewall (1994), Shanahan (1997), and Reiter (2001). Most theories treat events1 deductively, along the lines of the representation of actions used in the planner strips (Fikes & Nilsson, 1971). Each event type is defined by its preconditions and effects. For example, in the blocks world, the preconditions for unstacking block x from block y are that x is on y, x is clear (no block is on top of it), and the robot hand is empty. The effects are that the hand is holding x, y is clear, and each of the preconditions is false. Change is then a matter of deduction. If a particular event (a token of an event type) occurs and its particular preconditions hold, then its particular effects are deduced, and so necessarily follow, from it.