Primary and Secondary Plan Diagnosis∗

Diagnosis of plan failures is an important subject in both singleand multi-agent planning. Plan diagnosis may provide information that can improve the way the plan failures are dealt with in three ways: (i) it provides information necessary for the adjustment of the current plan or for the development of a new plan, (ii) it can be used to point out which equipment and/or agents should be repaired or adjusted so they will not further harm the plan execution, and (iii) it can identify the agents responsible for plan execution failures. We introduce two general types of plan diagnosis: primary plan diagnosis identifying the incorrect or failed execution of actions, and secondary plan diagnosis that identifies the underlying causes of the faulty actions. Furthermore, three special cases of secondary diagnosis are distinguished, namely equipment diagnosis, environment diagnosis and agent diagnosis.