Plan reversals for recovery in execution monitoring

In this paper, we introduce a new method to recover from discrepancies in a general monitoring framework where the agent finds some explanations (points of failure) for discrepancies. According to this method, the agent finds a reverse plan to backtrack to a diagnosed point of failure and subsequently continues with the original plan. This method is appealing given that such a reverse plan is short with respect to the overall plan to be executed. While a reverse plan could be computed online by solving a planning problem, we present a potentially more efficient method: We first build offline a reverse plan library by finding reverse plans for action sequences, and then use this library online to construct reverse plans. The former part is done by reducing the problem of finding pairs of action sequences and reverse plans (of a certain length) to a conformant planning problem; for the latter, we present a polynomial time algorithm. Furthermore, we analyze the complexity of finding reverse plans, and obtain that the presented reduction is reasonable in general.