Petri Nets Unfoldings and the individual/collective token philosophy

The notion of unfolding plays a major role in the so called non sequential semantics of Petri nets. In literature various approaches to this notion have been proposed, taking into account the so called individual token philosophy (the whole history is relevant) and the so called collective token philosophy (part of the history can be forgotten). In this paper we compare and relate two notions of unfolding (one for the individual and the other for the collective token philosophy) and we investigate on the relations between these two approaches and the non sequential behaviour of Petri Nets.