Diagnosis of plan step errors and plan structure violations

Failures in plan execution can be attributed to errors in the execution of plan steps or violations of the plan structure. While in previous work we have concentrated on the first type of failures, in this paper we introduce the idea of diagnosing violations in the plan structure. The structure of a plan prescribes which actions have to be performed and which precedence constraints between them have to be respected. Especially in multiagent environments violations of plan structure might easily occur as the consequence of synchronization errors. Using a formal framework for plan diagnosis, we show how Model-Based Diagnosis can applied to identify these violations of plan structure specifications and we analyze the computational complexity of the associated diagnostic problems.