Simulation-Based Diagnosis

Abstract

The diagnostic techniques presented in Chapters 4 and 5, either monolithic or modular, are applicable to a class of DESs with asynchronous behavior, where the system reaction is a sequence of component transitions. Thus, it is not possible for two or more component transitions to be fired in parallel. By contrast, in a synchronous DES all the triggerable transitions are fired in parallel. The reaction is a sequence of system transitions, each being a group of component transitions. A polymorphic DES integrates both synchronous and asynchronous behavior. The type of behavior is established by the type of the links wherein events are ready. A link can be either synchronous or asynchronous. At each point of the system reaction, transitions triggered by events that are ready on synchronous links have higher priority than transitions triggered by events on asynchronous links. Thus, if there is a synchronous link with a ready event, the system transition will be synchronous (including all the triggerable component transitions), otherwise it will be asynchronous (including just a component transition) . Both monolithic and modular diagnostic approaches are extended for polymorphic systems. In particular, since a system transition may involve several observable component transitions, the signature of the system reaction is a sequence of sets of messages. However, the observation relevant to a diagnostic problem is still structured as a collection of items, each being a sequence of messages. The distillation of the diagnostic information from the active space follows the same pattern adopted for active systems.