Reasoning about Complex Actions with Incomplete Knowledge: A Modal Approach

In this paper we propose a modal approach for reasoning about dynamic domains in a logic programming setting. We present a logical framework for reasoning about actions in which modal inclusion axioms of the form 〈p0〉φ ⊂ 〈p1〉〈p2〉 . . . 〈pn〉φ allow procedures to be defined for building complex actions from elementary actions. The language is able to handle knowledge producing actions as well as actions which remove information. Incomplete states are represented by means of epistemic operators and test actions can be used to check whether a fluent is true, false or undefined in a state. We give a non-monotonic solution for the frame problem by making use of persistency assumptions in the context of an abductive characterization. A goal directed proof procedure is defined, which allows reasoning about complex actions and generating conditional plans.