Nondeterminism avoidance in compositional synthesis of discrete event systems

Mohajerani, Sahar; Malik, Robi; Fabian, Martin

doi:10.1109/case.2011.6042432

Cited by 5 publications

(14 citation statements)

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“…The synthesis observation equivalence and weak synthesis observation equivalence algorithms have been implemented in the DES software tool Supremica (Åkesson et al, 2006). They are used for abstraction within a compositional supervisor synthesis algorithm that computes modular supervisors for large systems (Mohajerani et al, 2011a). This program has been used to compute synthesis abstractions for a set of benchmark examples that include complex industrial models and case studies taken from various application areas such as manufacturing systems and automotive body electronics.…”

Section: Resultsmentioning

confidence: 99%

“…Compositional methods are of great interest in supervisory control theory (Ramadge and Wonham, 1989), firstly in order to find more comprehensible supervisor representations, and secondly to overcome the problem of state-space explosion for systems with a large number of components. Compositional synthesis (Flordal et al, 2007;Malik and Flordal, 2008;Mohajerani et al, 2011a) seeks to compute a supervisor for a large discrete event system by abstraction. Individual system components are replaced by simpler versions obtained from abstraction, and synchronous composition is computed step-by-step on abstracted components.…”

Section: Introductionmentioning

confidence: 99%

“…More recently (Mohajerani et al, 2011b) proposed synthesis observation equivalence, a stronger version of observation equivalence that is adequate for compositional synthesis of least restrictive supervisors. The approach has been integrated in a framework with other abstraction methods and can be used to compute supervisors for practical applications (Mohajerani et al, 2011a). This paper proposes a relaxation of synthesis observation equivalence, called weak synthesis observation equivalence, which allows to achieve more abstraction.…”

Section: Introductionmentioning

confidence: 99%

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An Algorithm for Weak Synthesis Observation Equivalence for Compositional Supervisor Synthesis

Mohajerani

Malik

Fabian

2012

IFAC Proceedings Volumes

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This paper proposes an algorithm to simplify automata in such a way that compositional synthesis results are preserved in every possible context. It relaxes some requirements of synthesis observation equivalence from previous work, so that better abstractions can be made. The paper describes the algorithm, adapted from known bisimulation equivalence algorithms, for the improved abstraction method. The algorithm has been implemented in the DES software tool Supremica and has been used to compute modular supervisors for several large benchmark examples. It successfully computes modular supervisors, even for systems with more than 10 12 reachable states.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An Algorithm for Weak Synthesis Observation Equivalence for Compositional Supervisor Synthesis

Mohajerani

Malik

Fabian

2012

IFAC Proceedings Volumes

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“…Supervision equivalence [3] allows for transition removal, but relies on additional state labels that make some desirable abstractions impossible. The methods [6], [7] avoid event hiding that may cause problems in synthesis abstraction, but these approaches make it difficult to remove transitions.…”

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confidence: 99%

Transition removal for compositional supervisor synthesis

Mohajerani

Malik

Fabian

2012

2012 IEEE International Conference on Automation Science and Engineering (CASE)

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This paper investigates under which conditions transitions can be removed from an automaton while preserving important synthesis properties. The work is part of a framework for compositional synthesis of least restrictive controllable and nonblocking supervisors for modular discrete event systems. The method for transition removal complements previous results, which are largely focused on state merging. Issues concerning transition removal in synthesis are discussed, and redirection maps are introduced to enable a supervisor to process an event, even though the corresponding transition is no longer present in the model. Based on the results, different techniques are proposed to remove controllable and uncontrollable transitions, and an example shows the potential of the method for practical problems. I. INTRODUCTION Supervisory control theory [1] provides a general framework to compute least restrictive strategies to control a given plant such that its behaviour satisfies a given specification. Synthesis for systems with a large number of components is impeded by an inherent complexity problem known as state-space explosion. A lot of research has been devoted to overcome the state-space explosion problem, and also to find more comprehensible supervisors [1]-[3]. Compositional methods seek to avoid large state spaces using abstraction, and have been used in verification [4], [5] and synthesis [3], [6], [7]. In a system with a large number of components, it is often possible to simplify individual components before composing them with the rest of the system, achieving significant performance improvements. Several ways to simplify components have been investigated in recent years. Natural projection is a standard and effective way to compute abstractions, although strong restrictions need to be imposed to ensure the preservation of synthesis results [8], [9]. Observation equivalence [10] and conflict equivalence [11] are well-known abstraction methods for nonblocking verification [5], but for synthesis these abstractions can only be applied in combination with unobservable events [12], [13], which limits their applicability. Recently, frameworks for compositional synthesis based on abstractions of nondeterministic automata have been proposed [3], [6], [7], in some cases showing substantial reduction of the number of states encountered during synthesis. This paper seeks to enhance these methods by providing means to remove transitions. This is important, because for This work was supported by the Swedish Research Council.

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“…Researchers are seeking effective control methods for various subclasses of DES that enjoy special structures. Such structures will admit modularity [13], [14], [15], [16] and model abstraction [17], [18], [19], [20] to circumvent computing global dynamic models.…”

Section: Introductionmentioning

confidence: 99%

Supervisory control of extended finite automata using transition projection

Shoaei

Feng

Lennartson

2012

2012 IEEE 51st IEEE Conference on Decision and Control (CDC)

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Abstract-A limitation of the Ramadge and Wonham (RW) framework for the supervisory control theory is the explicit state representation using finite automata, often resulting in complex and unintelligible models. Extended finite automata (EFAs), i.e., deterministic finite automata extended with variables, provide compact state representation and then make the control logic transparent through logic expressions of the variables. A challenge with this new control framework is to exploit the rich control structure established in RW's framework. This paper studies the decentralized control structure with EFAs. To reduce the computational complexity, the controller is synthesized based on model abstraction of subsystems, which means that the global model of the entire system is unnecessary. Sufficient conditions are presented to that guarantee the decentralized supervisors result in maximally permissive and nonblocking control to the entire system.

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Nondeterminism avoidance in compositional synthesis of discrete event systems

Cited by 5 publications

References 14 publications

An Algorithm for Weak Synthesis Observation Equivalence for Compositional Supervisor Synthesis

An Algorithm for Weak Synthesis Observation Equivalence for Compositional Supervisor Synthesis

Transition removal for compositional supervisor synthesis

Supervisory control of extended finite automata using transition projection

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