Observability in interpreted Petri nets using sequence invariants

This paper addresses the observability problem in discrete event systems modeled by interpreted Petri net (IPN). The concepts of input and output sequence invariants of an IPN are Introduced. These sequence invariants are used to state a characterization of observable IPN, which is similar to the one presented for continuous systems using a geometric approach. However, since the computation of sequence invariants is computationally hard, the characterization of observable IPN using sequence invariants is turned into a characterization based on the notions of event-detectability and marking-detectability.