In: Rozenberg, G.: Lecture Notes in Computer Science, Vol. 340: Advances in Petri Nets 1988, pages 331-342. Springer-Verlag, 1988.
Abstract: Processe of arbitrary EN-systems are defined as traces over the total alphabet of events and conditions; they are called occurrence traces. The class of the EN-systems is characterized, which processes are labelled occurrence nets; it properly contains the class of contact-free EN-systems.