Reasoning About Action II: The Qualification Problem

We present a computationally eeective approach to representing and reasoning about actions with many qualiications. The approach involves treating actions as qualiied not by speciic facts that may or may not hold when the action is executed, but instead as potentially qualiied by general constraints describing the domain being investigated. Speciically, we suggest that the result of the action be computed without considering these qualifying domain constraints, and take the action to be qualiied if and only if any of the constraints is violated after the computation is complete. Our approach is presented using the framework developed in 6], where we discussed a solution to the frame and ramiication problems based on the notion of possible worlds, and compared the computational requirements of that solution to the needs of more conventional ones. In the present paper, we show that the domain constraint approach to qualiication, coupled with the possible worlds approach described earlier, has the remarkable property that essentially no computational resources are required to connrm that an action is unqualiied. As before, we also make a quantitative comparison between the resources needed by our approach and those required by other formulations.