DISCRETE-EVENT REPRESENTATION OF QUALITATIVE MODELS USING PETRI NETS

The paper discusses how Petri nets may be used for the qualitative mod eling of physical systems. The qualitative state of a system is repres ented by the marking of the net. The crossing of a landmark value corr esponds to the firing of a transition. We give a formal procedure to c onstruct a Petri net model corresponding to a given set of qualitative equations. The approach can be used to study both autonomous systems and systems with forcing inputs. The dynamic behavior of the system ca n be studied as sequences of reachable markings of the net and can be computed with standard Petri net execution techniques. This approach a lso leads to a simple framework for the study of hybrid systems, i.e., systems whose behavior is described by both continuous and discrete e vent dynamics. Several examples, with applications to diagnosis and co ntrol, are fully discussed.