Rationale-Based Monitoring for Planning in Dynamic Environments

We describe a framework for planning in dynamic environments. A central question is how to focus the sensing performed by such a system, so that it responds appropriately to relevant changes, but does not attempt to monitor all the changes that could possibly occur in the world. To achieve the required balance, we introduce rationale.based monitors, which represent the features of the world state that are included in the plan rationale, i.e., the reasons for the plannln~ decisions so far made. Rationalebased monitors capture information both about the plan currently under development and the alternative choices that were found but not pursued. We discuss the plan transformations that may result from the firing of a rationale-based monitor, for example when an alternative choice is detected. We have implemented the generation of and response to rationale-based monitoring within the Prodigy planner, and we describe experiments that show the feasibility of our approach.