  Supervisory control theory provides means to synthesize supervisors for
systems with discrete-event behavior from models of the uncontrolled plant and
of the control requirements. The applicability of supervisory control theory
often fails due to a lack of scalability of the algorithms. The paper proposes
a format for the requirements and a method to ensure that the crucial
properties of controllability and nonblockingness directly hold, thus avoiding
the most computationally expensive parts of synthesis. The method consists of
creating a control problem dependency graph and verifying whether it is
acyclic. Vertices of the graph are modular plant components, and edges are
derived from the requirements. In case of a cyclic graph, potential blocking
issues can be localized, so that the original control problem can be reduced to
only synthesizing supervisors for smaller partial control problems. The
strength of the method is illustrated on two case studies: a production line
and a roadway tunnel.
