Computing hierarchical nonblocking discrete event systems

We develop two new procedures for the discrete event system (DES) software package TCT. Each is useful in the context of working with hierarchical DES, where 'high-level' model abstractions are used to synthesize control action for the original, more complex, 'low-level' plant. The first procedure tests whether or not a DES satisfies the observer property. If it fails to, then its high-level transition structure is modified so that it does. The second procedure tests a DES for the hierarchical nonblocking (HNB) property. When the test is inconclusive the original DES is modified to ensure this property. Each is accompanied by a thorough complexity study and examples to illustrate its utility. We also discuss the pros and cons of various HNB control architectures.