Transforming hierarchical concepts of GRAFCET into a suitable Petri net formalism

GRAphe Fonctionnel de Commande Etape Transition (GRAFCET) is a powerful graphical means for the specification of controllers in discrete event systems and an international standard since 1988. GRAFCET contributes to a more structural and model driven approach in the design of logic controllers but still lacks an exhaustive formal definition. As a step towards an exhaustive formal model of GRAFCET, some ambiguities of the standard's definitions have to be discussed with regard to means of hierarchical structuring, namely enclosing and forcing. Based on this discussion, the authors propose an extension of a formal model for GRAFCET as a control interpreted Petri net (CIPN).