Monitoring Discrete Event Systems Using Petri Net Embeddings

Abstract

In this paper we discuss a methodology for monitoring failures and other activity in discrete event systems that are described by Petri nets. Our method is based on embedding the given Petri net model in a larger Petri net that retains the functionality and properties of the given one, perhaps in a non-separate (that is, not immediately identifiable) way. This redundant Petri net embedding introduces “structured redundancy” that can be used to facilitate fault detection, identification and correction, or to offer increased capabilities for monitoring and control. We focus primarily on separate embeddings in which the functionality of the original Petri net is retained in its exact form. Using these embeddings, we construct monitors that operate concurrently with the original system and allow us to detect and identify different types of failures by performing consistency checks between the state of the original Petri net and that of the monitor. The methods that we propose are attractive because the resulting monitors are robust to failures, they may not require explicit acknowledgments from each activity, and their construction is systematic and easily adaptable to restrictions in the available information. We also discuss briefly how to construct non-separate Petri net embeddings.