Hierarchical Interface-Based Supervisory Control (HISC) decomposes a discrete-event system (DES) into a high-level subsystem which communicates with n >= 1 low-level subsystems, through separate interfaces.  It provides a set of local conditions that can be used to verify global conditions such as nonblocking and controllability such that the complete system model never needs to be constructed.

 

Currently, a designer must create the supervisors  himself and then verify that they satisfy the HISC conditions.   In this paper, we develop a synthesis method that  can take advantage of the HISC  structure. We replace the supervisor for each level by a corresponding specification DES.  We  then construct for each level  a maximally permissive supervisor that satisfies the corresponding HISC conditions.

 

We define a set of language based fixpoint operators and show that they compute the required level-wise supremal languages. We then discuss the complexity of our algorithms and  show that they potentially offer significant savings over  the monolithic approach. We also briefly discuss a symbolic HISC verification and synthesis method  using Binary Decision Diagrams, that we have also developed. 

 

A large manufacturing system example (worst case state space on the order of 10^30) extended from the AIP example is briefly discussed. The example showed that  we can now handle  a given level with a statespace as large as 10^15 states, using less than 160MB of memory. This represents a significant improvement in the size of systems that can be handled by the HISC approach. A software tool for synthesis and verification of HISC systems using our approach was also developed.