Discrete Event System Theory Research Articles

Metric for Calculation of System Complexity based on its Connections

This paper proposes a methodology based on system connections to calculate its complexity. Two study cases are proposed: the dining Chinese philosophers’ problem and the distribution center. Both studies are modeled using the theory of Discrete Event Systems and simulations in different contexts were performed in order to measure their complexities. The obtained results present i) the static complexity as a limiting factor for the dynamic complexity, ii) the lowest cost in terms of complexity for each unit of measure of the system performance and iii) the output sensitivity to the input parameters. The associated complexity and performance measures aggregate knowledge about the system.

A Discrete Event System approach to On-line Testing of digital circuits with measurement limitation

In the present era of complex systems like avionics, industrial processes, electronic circuits, etc., on-the-fly or on-line fault detection is becoming necessary to provide uninterrupted services. Measurement limitation based fault detection schemes are applied to a wide range of systems because sensors cannot be deployed in all the locations from which measurements are required. This paper focuses towards On-Line Testing (OLT) of faults in digital electronic circuits under measurement limitation using the theory of discrete event systems. Most of the techniques presented in the literature on OLT of digital circuits have emphasized on keeping the scheme non-intrusive, low area overhead, high fault coverage, low detection latency etc. However, minimizing tap points (i.e., measurement limitation) of the circuit under test (CUT) by the on-line tester was not considered. Minimizing tap points reduces load on the CUT and this reduces the area overhead of the tester. However, reduction in tap points compromises fault coverage and detection latency. This work studies the effect of minimizing tap points on fault coverage, detection latency and area overhead. Results on ISCAS89 benchmark circuits illustrate that measurement limitation have minimal impact on fault coverage and detection latency but reduces the area overhead of the tester. Further, it was also found that for a given detection latency and fault coverage, area overhead of the proposed scheme is lower compared to other similar schemes reported in the literature.

Individuals, populations and fluid approximations: A Petri net based perspective

Discrete Event Systems (DES) theory and engineering are mainly driven by needs that arise in many different human-made systems (manufacturing, communications, logistics, workflow management, traffic, etc.). With the accelerated increase in the complexity and size of new technological constructions, the state explosion problem in DES analysis and synthesis becomes more and more acute.Two traditional conceptual and complementary ways of dealing with the computational complexities in the Petri nets (PN) framework are structure theory (that investigates the relationship between the behavior of a net system and its structure) and fluid relaxations, here leading to particular classes of hybrid systems. In the second case, the expected computational gains for analysis and synthesis problems are usually achieved at the expense of the fidelity or accuracy of the relaxed model. This invited overview will mainly focus on the second strategy, nevertheless always interspersed with basic structural concepts and methods. Using an example-driven approach, starting with a DES “view of the system”, the legitimization and improvement of fluidization process, the aggregation of local states by symmetries and the decolorization of models will be briefly addressed, together with reflections about the analysis of the new models obtained.As the linearization of a continuous dynamical system, the fluidization of a DES is a relaxation that has to be used with care, depending on the problem at hand. This abstraction is here considered from two complementary perspectives: at logical and at performance levels, both for untimed and timed PNs. On the one hand, the expressive power of timed fluid PNs under infinite server semantics is such that the simulation of Turing machines is possible. From a complementary perspective, the expression of modeling capabilities such as non-monotonicities and bifurcations may also be revealed for steady-state behaviors. Symmetries (more generally, lumping) seek to group together “equivalent” behaviors and decolorization seeks to abstract identities, in order to create new collectivities of processes and resources. The synergy between symmetry-decolorization state-aggregation approaches and fluid relaxations is highlighted. In fact, the first approaches not only reduce the state space, but also “produce” populations, thus proceed upgrading the applicability of fluidization. Opening the window, related issues such as control, optimization, observation or diagnosis are briefly pointed out. For conciseness, this work is limited to fully fluid (or continuous) PN models and their relationships with the corresponding discrete systems.

Modeling and Simulating for Emergency Medical Service System Optimizing Based on Discrete Event System Theory

Due to the complexity and randomness of emergency demands, it is difficult to describe and analyze the Emergency Medical Service Systems (EMSS) just by certain modeling. Therefore, a stochastic modeling and simulating method for EMSS optimizing is proposed based on the Discrete Event System theory. With a fictive and stochastic medical emergency scenario, the relevant simulation model is constructed with the FLEXSIM software quickly and explicitly. And by simulating and analyzing, it is easily to discover the bottlenecks and to optimize the EMSS system.

Modeling and Supervisory Control of Mobile Robots: A Case of a Sumo Robot

Abstract: This paper presents a methodology for modeling and controlling autonomous mobile robots and illustrates this approach using a sumo robot problem. The free behavior of the robot and its control specifications are modeled by finite state machines, and the supervisory control theory of discrete event systems is used to obtain the logical behavior of the robot in closed-loop. We also present a proposal for implementing the control structure obtained by the presented approach.

Real-time management of complex resource allocation systems: Necessity, achievements and further challenges

Many contemporary applications, ranging from flexibly automated production systems, to automated material handling and intelligent transportation systems, to internet-based workflow management systems, and more recently, to the massively parallelized software systems that emerge in the context of the novel multi-core computing architectures, can be perceived as a set of finite resources that support a number of concurrently running processes. These processes execute in a staged manner and, at each stage, they vie for the allocation of various subsets of the system resources. To effectively support and manage the extensive levels of concurrency and operational flexibility that are contemplated for these environments, and the ensuing complexity, there is a substantial need for formal models and tools that will enable the modeling, analysis and eventually the control of the aforementioned resource allocation function so that the resulting dynamics are, both, behaviorally correct and operationally efficient. This article overviews a research program that seeks to address the aforementioned need by using the unifying abstraction of the resource allocation system (RAS) and supporting modeling frameworks, like automata, Petri nets, and Markov reward and decision processes, borrowed from the area of Discrete Event Systems (DES) theory. The presented results take advantage of the special structure that exists in the considered RAS classes, and they are characterized by their analytical rigor and computational tractability. The article also highlights the further challenges that must be addressed for the successful completion and promotion of the pursued framework.

Control of Flexible Manufacturing Systems under model uncertainty using Supervisory Control Theory and evolutionary computation schedule synthesis

A new approach for the problem of optimal task scheduling in flexible manufacturing systems is proposed in this work, as a combination of metaheuristic optimization techniques with the supervisory control theory of discrete-event systems. A specific encoding, the word-shuffling encoding, which avoids the generation of a large number of infeasible sequences, is employed. A metaheuristic method based on a Variable Neighborhood Search is then built using such an encoding. The optimization algorithm performs the search for the optimal schedules, while the supervisory control has the role of codifying all the problem constraints, allowing an efficient feasibility correction procedure, and avoiding schedules that are sensitive to uncertainties in the execution times associated with the plant operation. In this way, the proposed methodology achieves a system performance which is typical from model-predictive scheduling, combined with the robustness which is required from a structural control.

Supervisory Control of Fuzzy Discrete-Event Systems for Simulation Equivalence

The supervisory control theory of fuzzy discrete event systems (FDESs) for fuzzy language equivalence has been developed. However, in a way, language equivalence has limited expressiveness. So if the given specification can not be expressed by language equivalence, then the control for language equivalence does not work. In this paper, we further establish the supervisory control theory of FDESs for fuzzy simulation equivalence whose expressiveness is stronger than that of fuzzy language equivalence. First, we formalize the notions of fuzzy simulation and fuzzy simulation equivalence between two FDESs. Then we present a method for deciding whether there is a fuzzy simulation or not. In addition, we also show several basic properties of fuzzy simulation relations. Afterwards, we put forward the notion of fuzzy simulation-based controllability, and particularly show that it serves as a necessary and sufficient condition for the existence of the fuzzy supervisors of FDESs. Moreover, we study the "range" control problem of FDESs. Some examples are given to illustrate the main results obtained.

Supervisory Control of DES With Extended Finite-State Machines and Variable Abstraction

This paper deals with two relevant aspects of Supervisory Control Theory (SCT) of Discrete Event Systems: the difficulty faced to model specifications to be fulfilled by the system under control, and the computational cost to synthesize supervisors. These aspects are addressed by Extended Finite-state Machines (EFSMs), a version of ordinary finite-state machines, extended with variables. EFSMs have been used in SCT to facilitate modeling tasks, but they are not directly advantageous in synthesis. This paper shows that some variables can nevertheless be abstracted from an EFSM to compute a supervisor. The proposed approach has the modeling benefits of EFSMs while preserving controllability and least restrictiveness of control solutions, and the synthesis procedure can be conducted with computational gains. An algorithm to compute supervisors from abstractions is also proposed. A way to construct abstractions that always lead to optimal synthesis complements the contributions, which are illustrated by two examples of manufacturing systems.

Real-Time Management of Complex Resource Allocation Systems: Necessity, Achievements and Further Challenges

Abstract: Many contemporary applications, ranging from flexibly automated production systems, to automated material handling and intelligent transportation systems, to internetbased workflow management systems, and more recently, to the massively parallelized software systems that emerge in the context of the novel multi-core computing architectures, can be perceived as a set of finite resources that support a number of concurrently running processes; these processes execute in a staged manner and vie for the allocation of various subsets of the system resources. To effectively support and manage the extensive levels of concurrency and operational flexibility that are contemplated for these environments, and the ensuing complexity, there is a substantial need for formal models and tools that will enable the modeling, analysis and eventually the control of the aforementioned resource allocation function so that the resulting dynamics are, both, behaviorally correct and operationally efficient. This write-up overviews a research program that seeks to address the aforementioned need by using the unifying abstraction of the resource allocation system (RAS) and supporting modeling frameworks, like automata, Petri nets, and Markov reward and decision processes, borrowed from the area of Discrete Event Systems (DES) theory. The presented results take advantage of the special structure that exists in the considered RAS classes, and are further characterized by, both, their analytical rigor and computational tractability. The write-up also highlights the further challenges that must be addressed for the successful completion and promotion of the pursued framework.

Petri nets for the control of discrete event systems

The interest in Petri nets has grown within the automatic control community in parallel with the development of the theory of discrete event systems. In this article, our goal is to give a flavor of the features that make Petri nets a good model for discrete event systems and to point out the main areas where Petri nets have offered the most significant contributions.

자동화 시스템의 관리제어 설계를 위한 새로운 모듈화 기법

This paper describes the application of discrete event systems theory to the design of an automated laboratory system. Current automated laboratory systems typically consist of several interacting processes that must be carefully sequenced to avoid any possible process conflicts. Discrete Event Systems (DES) theory and Supervisory Control Theory (SCT) can be applied together as effective methods of modeling the system dynamics and designing supervisory controllers to precisely sequence the many processes that such systems might involve. Classical approaches to supervisory controller design tend to result in complex controller structures that are difficult to implement, maintain, and upgrade. In this paper, a new approach to designing supervisory controllers for automated laboratory systems is introduced. This new approach uses a modular controller structure that is easier to implement, maintain, and upgrade,and deals with state explosion issues in a novel and efficient way.

Política de despacho para evitar bloqueos en celdas de manufactura flexible del tipo multi-reentrante

<p>Una Celda de Manufactura Flexible (CMF) se puede modelar usando la teoría pertinente a sistemas de eventos discretos. La CMF integra un conjunto de recursos, operaciones y materias primas que se combinan para la elaboración de productos. Si esos recursos no se controlan adecuadamente, la CMF se bloqueará. Con el fin de evitar dicho bloqueo, en este trabajo se presentan cuatro lineamientos para construir una política de asignación de recursos a partir del estudio básico de esperas circulares y prioridades de producción. Para elaborar una CMF teórica planteada por Peng y Zhou (2003), y desde los lineamientos propuestos, se construyó una política de despacho y se efectuaron simulaciones de la celda de manufactura con y sin controlador. Como resultado, la política de despacho logró realizar las asignaciones de recursos en forma adecuada para el ensamblaje de las partes.</p>

An algorithm to test the conflict preorder

This paper proposes a way to effectively compare the potential of processes to cause conflict . In discrete event systems theory, two concurrent systems are said to be in conflict if they can get trapped in a situation where they are both waiting or running endlessly, forever unable to complete their common task. The conflict preorder is a process-algebraic pre-congruence that compares two processes based on their possible conflicts in combination with other processes. This paper improves on previous theoretical descriptions of the conflict preorder by introducing less conflicting pairs as a concrete state-based characterisation. Based on this characterisation, an effective algorithm is presented to determine whether two processes are related according to the conflict preorder.

권력에 기초한 이산사건시스템의 관리제어: 정치경제학 해석

본 논문에서는 이산사건시스템의 관리제어이론을 정치경제학에서 권력의 문제를 해석하는데 응용할 수 있음을 보인다. 이를 위해 권력에 기초한 제어입력의 결정 메커니즘과 이를 통한 관리제어시스템의 동작을 정의한다. 구체적으로, 경쟁하는 집단들(제어기들)의 공통 제어목적을 달성하기 위한 필요 충분 조건으로 권력-제어가능성의 개념을 소개한다. 이 조건이 만족되면 정해진 권력함수를 가진 집단들의 모듈러 제어를 통해 제어된 시스템은 공통의 제어목적을 벗어나지 않는다.

Verification of Opacity and Diagnosability for Pushdown Systems

In control theory of discrete event systems (DESs), one of the challenging topics is the extension of theory of finite-state DESs to that of infinite-state DESs. In this paper, we discuss verification of opacity and diagnosability for infinite-state DESs modeled by pushdown automata (called here pushdown systems). First, we discuss opacity of pushdown systems and prove that opacity of pushdown systems is in general undecidable. In addition, a decidable class is clarified. Next, in diagnosability, we prove that under a certain assumption, which is different from the assumption in the existing result, diagnosability of pushdown systems is decidable. Furthermore, a necessary condition and a sufficient condition using finite-state approximations are derived. Finally, as one of the applications, we consider data integration using XML (Extensible Markup Language). The obtained result is useful for developing control theory of infinite-state DESs.

On the Modeling and Control of Discrete Event Systems Theory

On the Modeling and Control of Discrete Event Systems Theory

A modelling approach to Service oriented Architecture for on-line diagnosis

Failure diagnosis is one of the key challenges of Service oriented Architectures. One of the methods of identifying occurrences of failure is to use Diagnosers; software modules or services are deployed with the system to monitor the interaction between services for identifying whether a failure has happened or may have happened. This paper aims to present a suitable modelling framework to allow automated creation of Diagnosers based on Discrete Event System (DES) theory. Coming up with an appropriate modelling language framework is a prerequisite to applying DES techniques. Modelling languages popular in DES, such as Petri nets and automata, despite being sufficiently adequate for modelling, are not well adopted by the SoA community. Inspired by Petri nets and Workflow Graph, the modelling suggested in this paper closely follows BPEL that is widely used by the community. In particular, our language includes constructs that are supported by major tool vendors. To demonstrate that the suggested formal language is a suitable basis for the application of DES theory, we have extended one of the existing DES methods for the creation of centralised Diagnoser. Two algorithms for creating Diagnosers are put forward. These algorithms are applied into the models that are abstracted from the BPEL representation of the involving services. As a proof of concept, an implementation of the suggested approach is created as an Oracle JDeveloper plugin that automatically produces new Diagnosing services and integrates them to work with existing services. The paper ends with a series of empirical results on the performance-related aspects of the proposed method.

Emergence in stigmergic and complex adaptive systems: A formal discrete event systems perspective

Complex systems have been studied by researchers from every discipline: biology, chemistry, physics, sociology, mathematics and economics and more. Depending upon the discipline, complex systems theory has accrued many flavors. We are after a formal representation, a model that can predict the outcome of a complex adaptive system (CAS). In this article, we look at the nature of complexity, then provide a perspective based on discrete event systems (DEVS) theory. We pin down many of the shared features between CAS and artificial systems. We begin with an overview of network science showing how adaptive behavior in these scale-free networks can lead to emergence through stigmergy in CAS. We also address how both self-organization and emergence interplay in a CAS. We then build a case for the view that stigmergic systems are a special case of CAS. We then discuss DEVS levels of systems specifications and present the dynamic structure extensions of DEVS formalism that lends itself to a study of CAS and in turn, stigmergy. Finally, we address the shortcomings and the limitation of current DEVS extensions and propose the required augmentation to model stigmergy and CAS.

Research on Modeling and Simulating of Discrete Event System Based on Petri Net

A framework of modeling and simulating a typical artificial system is proposed based on discrete event system and Petri net. Firstly, the system model is constructed based on discrete event system theory. Secondly, the model is described and analyzed by using Petri net. Then, the simulation procedures on Matlab platform are presented in detail. The proposed framework is applied to modeling and simulating a logical control system of a marine diesel engine. The simulation results indicate that this logical control system model can be constructed by the given framework and the proposed method is effective in simulating and analyzing this kind of artificial system.