Noninterference Enforcement via Supervisory Control in Bounded Petri Nets

State-Partition-Based Control of Discrete Event Systems for Enforcement of Regular Language Specifications

In this paper a hybrid approach is proposed for supervisory control of discrete event systems (DES) subject to forbidden states. Assuming that an uncontrolled bounded Petri net (PN) model of a (plant) DES and a set of forbidden state specifications are given, the proposed approach computes a maximally permissive and nonblocking closed-loop hybrid model. The first step is to simplify the given PN model by means of PN reduction rules. The simplified model and the specifications are then represented as buffers, and supervisory control theory (SCT) is applied to obtain a Ramadge–Wonham (RW) supervisor in the form of an automaton. After reduction of the latter’s state size by a ‘control congruence’, the simplified RW supervisor is represented by a so-called auto-net and coupled to the given uncontrolled PN plant model by means of inhibitor arcs to represent the disabling actions. The plant model and supervisor auto-net run concurrently, synchronizing on shared events. This procedure provides a maximally permissive and nonblocking ‘hybrid’ (mixed PN/automaton) closed-loop controlled system. The method is straightforward logically, graphically, and technologically. Its applicability is shown by two examples, one of them a workcell from the PN control literature.

This paper addresses the problem of current-state opacity of discrete event systems (DES) modeled with Petri nets. A system is said to be current-state opaque if the intruder who only has partial observations on the system's behavior is never able to infer that the current state of the system is within a set of secret states. Based on the notion of basis markings, an efficient approach to verifying current-state opacity in bounded Petri nets is proposed, without computing the whole reachability set or exhaustively enumerating the set of markings consistent with the observation. An example showing the efficiency of the approach is presented.

This paper presents a modular liveness-enforcing supervisory control design for scalable discrete event systems. A maximally permissive monitor-based supervisory control policy is suggested using divide and conquer paradigm. A vector-covering approach is used to minimize essential set of legal markings and first-met bad markings. Providing that modules of system interact by Enable operator, it will be proved that monitor-based supervisory control methods can be applied modularly. Then, Enable operator of Petri nets (PNs) can be used to synthesize subsystems. This algorithm is implemented by extending a graphical PN drawing and analysis tool with supervisory control analysis modules as Java codes. The experimental results show that this approach constitutes a primary step towards a hierarchical procedure that overcomes whole reachability graph computation, which is a bottleneck in deadlock preventing supervisory control policies.

Presently, the number, types, and distribution of resources in a resource allocation system (RAS), may change frequently and dynamically due to fluctuant customer demands. Such changes in a resource allocation (RA) specification mean different production or service behaviors yielded by the providers. This new situation gives rise to a challenging problem, namely, how to switch smoothly the provider systems to support different production. This paper tries to address this problem from the viewpoint of discrete event system (DES) supervisory control. A Petri net (PN) controller of an RAS can be designed from a resource allocation specification using P-invariant. Once the RA specification is changed, the controller is updated following it. Moreover, if the changed specification is unreasonable, the whole control system, are reconfigured to reach a legal system state and a newly reasonable resource allocation solution is re-calculated. Specifically, the paper proposed a reconfiguration method of a PN control system that is transformed into PN reachability analysis problem using a mathematic programming approach. In our method, not only the transition firing costs but also the steps of concurrent firing are taken into account to achieve an optimal reconfiguration solution. Finally, an example is provided for illustrating the application of the mentioned methods.

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

The behavior mapping of systems has undergone rapid change with advances in technology. The representation has become digital with state description of the behavior. This manifestation is called Discrete Event Systems (DES), exhibiting properties such as non – determinism, conflict and parallelism[1]-[3]. Supervisory Control Theory (SCT)[8],[9] is chosen as a modeling paradigm and Programmable Logic Controllers (PLC) [10] – [12] as an implementation tool for DES. This work investigates the use of Fuzzy Petri nets in supervisory control and suggests a modified and improved version called Fuzzy Automation Petri net (FAPN) as a modeling tool. It presents a systematic approach to the synthesis of Fuzzy Petri net based supervisor for the forbidden state problem using supervisory design procedure. The controlled model of the system can be constructed from this FAPN net structure. The implementation is using Flexible Manufacturing System (FMS) as an example of DES. The results can be interpreted and applied to high level manufacturing systems, where the role of the supervisor is to coordinate the control of multiple machines or to low level manufacturing systems, where the control function is to switch ON/OFF with respect to the dynamics between different valves.

This paper addresses the supervisory control of the class of discrete event system (DES) modeled by a Petri net. The control specification described by a linear 'less-than-or-equal-to' inequality defined on the place marking of the net has been extensively studied in the literatures. However, in this paper we consider the control specification in the form of linear 'greater-than-or-equal-to' marking inequality. The supervisory control of the DES with 'greater-than-or-equal-to' constraint is implemented via an enabling arc, which is a recently proposed arc by Uzam (1998) and Uzam et al. (1999) and can be regarded as complementarity of inhibitor arc. An example illustrates the supervisory control method is presented in this paper.

In this paper, the synthesis of bounded Petri nets from deterministic modal transition systems is shown to be undecidable. The proof is built from three components. First, it is shown that the problem of synthesising bounded Petri nets satisfying a given formula of the conjunctive nu-calculus (a suitable fragment of the mu-calculus) is undecidable. Then, an equivalence between deterministic modal transition systems and a language-based formalism called modal specifications is developed. Finally, the claim follows from a known equivalence between the conjunctive nu-calculus and modal specifications.

Discrete event systems in applications, such as industry and supply chain, may show a very complex behavior. For this reason, their design and operation may be carried out by the application of optimization techniques for decision making in order to obtain their highest performance. In a general approach, it is possible to implement these optimization techniques by means of the simulation of a Petri net model, which may require an intensive use of computational resources. One key factor in the computational cost of simulation‐based optimization is the size of the model of the system; hence, it may be useful to apply techniques to reduce it. This paper analyzes the relationship between two Petri net formalisms, currently used in the design of discrete event systems, where it is usual to count on a set of alternative structural configurations. These formalisms are a particular type of parametric Petri nets, called compound Petri nets, and a set of alternative Petri nets. The development of equivalent models under these formalisms and the formal proof of this equivalence are the main topics of the paper. The basis for this formal approach is the graph of reachable markings, a powerful tool able to represent the behavior of a discrete event system and, hence, to show the equivalence between two different Petri net models. One immediate application of this equivalence is the substitution of a large model of a system by a more compact one, whose simulation may be less demanding in the use of computational resources.

This paper presents an approach to perform Activity Based Costing (ABC) with Petri nets. ABC is a powerful methodology to calculate various of discrete event systems (e.g. production systems). Petri net models of discrete event systems are easy to create, comprehend, and to perform analysis, the mathematics behind Petri nets is also easy to grasp. This paper shows how ABC can be performed with Petri nets, so that various involved in a discrete event system can be easily measured with the help of the Petri net model. After a short introduction to ABC and Petri nets, this paper shows the approach which basically embeds various cost drivers as firing costs and firing times of transitions in a Petri net model. This work also presents a case study that is done with GPenSIM, a toolbox realized with this approach.

Diagnosability of faults in discrete event systems modeled with Petri nets can be assessed either via graph-based techniques (also called diagnoser, verifier/twin-plant based techniques), or via the solution of optimization problems. The approaches that belong to the former class are based on the analysis of the net reachability or coverability graphs (or of a more compact version of them). The latter approach exploits the mathematical representation of the net itself to specify and solve optimization problems, which are usually expressed as integer linear programming (ILP) problems. In this paper we exploit the railway Petri net model originally proposed in [16], and extended in [14] to be used as a benchmark for diagnosability analysis, to assess the efficiency of the approach based on the solution of ILP problems proposed in [3]. In order to show the effectiveness of the proposed technique, a comparison with a graph-based approach for analyzing diagnosability is also presented.

This paper addresses the problem of on-line identification of Discrete Event Systems (DES). A passive method for the progressive building of Petri net (PN) models from DES outputs evolution is presented. After introducing several concepts related with dynamical properties of DES, a learning algorithm that computes ordinary PN models according to the measurement of cyclic output streams is proposed. A procedure based on this algorithm can be on-line executed tracking the DES behavior from its output signals, whose durations are stored. The successive computed models tend progressively to represent the actual observed behavior.

Introduction to Discrete Event Systems is a comprehensive introduction to the field of discrete event systems, offering a breadth of coverage that makes the material accessible to readers of varied backgrounds. The book emphasizes a unified modeling framework that transcends specific application areas, linking the following topics in a coherent manner: language and automata theory, supervisory control, Petri net theory, Markov chains and queuing theory, discrete-event simulation, and concurrent estimation techniques. This edition includes recent research results pertaining to the diagnosis of discrete event systems, decentralized supervisory control, and interval-based timed automata and hybrid automata models.

A new method based on discrete event system is proposed for fault diagnosis of a certain kind of circuit, such as a relay control circuit. The original algorithm to obtain a minimal test set is improved. By using the improved algorithm the finest testable partition can be obtained and the complex testability analysis is avoided. The basic model of the proposed method and the general rule for fault diagnosis are described in detail. At first, the relay control circuit is described with corresponding combinational logic circuit model. Then, the fault diagnosis model of the circuit-under-test is constructed based on the given DES model. This method is applied to diagnose a relay control circuit. The results indicate that this method can diagnose this kind of circuit effectively and the new algorithm has a much lower computational complexity than the original algorithm. The fault elements can be localized exactly and this method has high practical value.