Modular feedback logic for discrete event systems
SIAM Journal on Control and Optimization
On the supermal controllable sublanguage of a given language
SIAM Journal on Control and Optimization
Decentralized supervisory control of discrete-event systems
Information Sciences: an International Journal - Robotics and Automation/Control Series
Supervisory Control of Distributed Systems: Conflict Resolution
Discrete Event Dynamic Systems
On the Computation of Observers in Discrete-Event Systems
Discrete Event Dynamic Systems
Designing communicating transaction processes by supervisory control theory
Formal Methods in System Design
On the Computation of Natural Observers in Discrete-Event Systems
Discrete Event Dynamic Systems
Discrete Event Dynamic Systems
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In the supervisory control of discrete-event systemsbased on controllable languages, a standard way to handle stateexplosion in large systems is by modular supervision: eitherhorizontal (decentralized) or vertical (hierarchical). However,unless all the relevant languages are prefix-closed, a well-knownpotential hazard with modularity is that of conflict. In decentralizedcontrol, modular supervisors that are individually nonblockingfor the plant may nevertheless produce blocking, or even deadlock,when operating on-line concurrently. Similarly, a high-levelhierarchical supervisor that predicts nonblocking at its aggregatedlevel of abstraction may inadvertently admit blocking in a low-levelimplementation. In two previous papers, the authors showed thatnonblocking hierarchical control can be guaranteed provided high-levelaggregation is sufficiently fine; the appropriate conditionswere formalized in terms of ’control structures‘ and ’observers‘.In this paper we apply the same technique to decentralized control,when specifications are imposed on ’local‘ models of the ’global‘process; in this way we remove the restriction in some earlierwork that the plant and specification (marked) languages be prefix-closed.We then solve a more general problem of ’coordination‘: namelyhow to determine a high level ’coordinator‘ that forestalls conflictin a decentralized architecture when it potentially arises, butis otherwise minimally ’intrusive‘ on low-level control action.Coordination thus combines both vertical and horizontal modularity.The example of a simple production process is provided as a practicalillustration. We conclude with an appraisal of the computationaleffort involved.