On Occurrence Net Semantics for Petri Nets with Contacts

. This paper is concerned with defining causal (non sequential) behavior of Petri nets via occurrence nets. Conventionally occurrence nets semantics is defined for contact-free Petri nets. In [8] E.Smith proposed non sequential semantics for nets with contacts. We present an alternative definition of occurrence nets semantic for nets with contacts, which gives a clear visual representation of concurrent process flow and maintains the correlation between causal and interleaving semantics of Petri nets. 1 Introduction Petri nets are a mathematical and graphical modelling tool for describing concurrent systems. Introduced in the sixties [2], since that time Petri nets proved to be one of the basic formal models for concurrent and distributed systems. Among many attractive features of Petri nets model is that it adopts both interleaving and causal formal semantics for describing its behavior. The causal semantics of Petri nets is represented by occurrence nets and concurrent runs ([4], cf..