HIERARCHICAL CONTROL OF DISCRETE-EVENT SYSTEMS

An abstract hierarchical control theory is developed for discrete-even t systems, based on the concepts of control structures and observers. Control structure is an abstract generalization of the family of contr ollable sublanguages in the Ramadge-Wonham framework. We establish a g eneral version of Zhong's hierarchical consistency by first achieving control consistency - preservation of control structures through the a ggregation mapping in a two-level hierarchy. For a refinement of hiera rchical consistency with preservation of nonblocking, the concept of o bserver is introduced via congruences on nondeterministic transition s tructures.