Giving back some freedom to the system designer

Organizational abstraction is proposed, together with functional abstraction, as a suitable means for disciplining concurrent system design by means of Superposed Automata (SA) nets, a subclass of Petri nets. Organizational abstraction is based on the notion of EB-equivalence, a less restrictive derivative of Milner's Observation Equivalence, and allows to disregard the internal organization of a system, taking into account the behaviour it exhibits to its environment only. Using both functional and organizational abstraction, it is possible to design a concurrent system without imposing any order in the way the subsequent SA net models are designed. The designed system in fact is independent, under very general conditions, from the intermediate steps that have been followed.