On the consistency of hierarchical supervision in discrete-event systems

Hierarchical structure in the supervisory control of discrete-event systems is formalized in the automaton framework of P.J. Ramadge and W.M. Wonham (SIAM J. Cont. Optimiz., vol.25, no.1, p.206-30, 1987). The setup embodies a low-level real-world model controlled by an operator and a high-level abstract model virtually controlled by a manager. The two levels are connected by command and information channels. Concepts of hierarchical consistency are proposed, relating high-level behavior required by the manager to low-level behavior achievable by the operator. It is shown that consistency can be realized by appropriately refining the information sent up by the operator to the manager