Embracing Causality in Specifying the Indirect Effects of Actions

Abstract

This paper considers the problem of specifying the effects of actions in the situation calculus using domain constraints. We argue that normal state constraints that refer to only the truth values of fluents are not strong enough for this purpose, and that a notion of causation needs to be employed explicitly. Technically, we introduce a new ternary predicate Caused into the situation calculus: Caused(p, v, s) if the proposition p is caused (by something unspecified) to have the truth value v in the state s. Using this predicate, we can represent not only action-triggered causal statements such as that the action load causes the gun to be loaded, but also fluent-triggered ones such as that the fact that the switch is in the up position causes the lamp to be on. The former is convenient for representing the direct effects of actions, and the latter the indirect effects.