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.