Verification Of Discrete Event Systems Research Articles

Diagnosability verification of discrete event systems

Fault diagnosis is one of the key topics in the study of computer program operation and automatic control of large complex systems these days. It can be used in wide-spanning areas. As early as the last century, researchers started to study diagnosis structures and made a series of progress. Moreover, the problem of diagnosability verification of a system received much attention from many researchers. Therefore, in this paper, a discrete event system (DES) is proposed and a diagnoser is constructed as an automaton model to verify the diagnosability of a given system. A method is proposed to test if a given system is diagnosable under the discrete event system structure. The states of a system are classified into three categories, and a diagnoser structure with basic algorithms and functions is defined to verify diagnosability. The proposed diagnoser structure can better capture the behavior of the system and verify its diagnosability.

Model Abstraction for Discrete-Event Systems Using a SAT Solver

Model abstraction for finite state automata is beneficial to reduce the complexity of discrete-event systems (DES), enhances the readability and facilitates the control synthesis and verification of DES. Supremal quasi-congruence computation is an effective way for reducing the state space of DES. Effective algorithms on the supremal quasi-congruence relation have been developed based on the graph theory. This paper proposes a new approach to translate the supremal quasi-congruence computation into a satisfiability (SAT) problem that determines whether there exists an assignment for Boolean variables in the state-to-coset allocation matrix. If the result is satisfied, then the supremal quasi-congruence relation exists and the minimum equivalence classes is obtained. Otherwise, it indicates that there is no such supremal quasi-congruence relation, and a new set of observable events needs to be modified or reselected for the original system model. The satisfiability problem on the computation of supremal quasi-congruence relation is solved by different methods, which are respectively implemented by mixed integer linear programming (MILP) in MATLAB, binary linear programming (BLP) in CPLEX, and a SAT-based solver (Z3Py). Compared with the MILP and BLP methods, the SAT method is more efficient and stable. The computation time of model abstraction for large-scale systems by Z3Py solver is significantly reduced.

New predictability verification tests for discrete-event systems modeled by finite state automata

Abstract This paper deals with the problem of copredictability verification of discrete event systems (DES) modeled by automata in less restrictive scenarios, i.e., avoiding the assumptions on language liveness and absence of cycles of states connected by unobservable events only. We present necessary and sufficient conditions for a regular language to be copredictable, and adapt previous results on diagnosability verification to develop two new strategies to verify copredictability: the first one is based on a diagnoser-like automaton, and the second one by using verifiers.

DEv-PROMELA: an extension of PROMELA for the modelling, simulation and verification of discrete-event systems

PROMELA is a well-known formalism for the modelling and the verification of concurrent systems. PROMELA deals with high-level specifications. As a result, PROMELA models are expressed in a high-level abstraction which does not consider explicit representation of time or events for example. But, the efficiency of the processes of verification and validation relies on the accuracy of the models. That is why we propose, in this paper, work to develop a new extension of PROMELA for the modelling of discrete-event systems. The verification of these models is then done by combining formal verification and simulation-based verification using SPIN and the tool DEv-PROMELA Studio, or using any existing DEVS simulators.

DEv-PROMELA: an extension of PROMELA for the modelling, simulation and verification of discrete-event systems

DEv-PROMELA: an extension of PROMELA for the modelling, simulation and verification of discrete-event systems

A framework for compositional nonblocking verification of extended finite-state machines

This paper presents a framework for compositional nonblocking verification of discrete event systems modelled as extended finite-state machines (EFSM). Previous results are improved to consider general conflict-equivalence based abstractions of EFSMs communicating both via shared variables and events. Performance issues resulting from the conversion of EFSM systems to finite-state machine systems are avoided by operating directly on EFSMs, deferring the unfolding of variables into state machines as long as possible. Several additional methods to abstract EFSMs and remove events are also presented. The proposed algorithm has been implemented in the discrete event systems tool Supremica, and the paper presents experimental results for several large EFSM models that can be verified faster than by previously used methods.

An algorithm for compositional nonblocking verification using special events

This paper proposes to improve compositional nonblocking verification of discrete event systems through the use of special events. Compositional verification involves abstraction to simplify parts of a system during verification. Normally, this abstraction is based on the set of events not used in the remainder of the system, i.e., in the part of the system not being simplified. Here, it is proposed to exploit more knowledge about the remainder of the system and check how events are being used. Always enabled events, selfloop-only events, failing events, and blocked events are easy to detect and often help with simplification even though they are used in the remainder of the system. Abstraction rules from previous work are generalised, and experimental results demonstrate the applicability of the resulting algorithm to verify several industrial-scale discrete event system models, while achieving better state-space reduction than before.

Comments on “Polynomial Time Verification of Decentralized Diagnosability of Discrete Event Systems” versus “Decentralized Failure Diagnosis of Discrete Event Systems”: Complexity Clarification

An article on codiagnosability verification of discrete event systems was reported by Moreira et al, claiming an improvement in complexity over a paper by Qiu and Kumar. This note clarifies an oversight in the complexity analysis of Moreira et al's paper. Further the results of Moreira et al's paper were obtained in a more restricted setting of “projection masks”, in contrast to the more general “non-projection masks” allowed in Qiu and Kumar's paper, which was overlooked. Finally in the special case when the projection masks are used, the complexity of Qiu and Kumar's paper is lower compared to the non-projection masks case, and equals the corrected complexity of Moreira et al's paper.

An Algorithm for Compositional Nonblocking Verification of Extended Finite-State Machines

This paper describes an approach for compositional nonblocking verification of discrete event systems modelled as extended finite-state machines (EFSM). Previous results about finite-state machines in lock-step synchronisation are generalised and applied to EFSMs communicating via shared variables. This gives rise to an EFSM-based conflict check algorithm that composes EFSMs gradually and partially unfolds variables as needed. At each step, components are simplified using conflict-equivalence preserving Abstract:ion. The algorithm has been implemented in the discrete event systems tool Supremica. The paper presents experimental results for the verification of two scalable manufacturing system models, and shows that the EFSM-based algorithm verifies some large models faster than previously used methods.

Introduction to the Special Issue on Modeling and Verification of Discrete Event Systems

Introduction to the Special Issue on Modeling and Verification of Discrete Event Systems

Monitoring of Temporal Requirements with Stocharts Observation Patterns, Application to a Level Crossing Control System

Works in the field of verification systems have shown the critical importance of time. The non-satisfaction of time may have important consequences for both security and performance points of view. For automated systems with level of security, the verification of time requirements is an essential part of the process validation system. In this paper, we are laying the foundations for a new and systematic approach for the verification of discrete event systems with time constraints. The contribution of this approach is threefold: first, unlike existing approaches, it allows for the verification of several requirements at once. Therefore, the approach is generic because we focus on developing mechanisms that take into account different types of requirements rather than the system to be verified. Finally, the implementation of the approach is almost as systematic because the verification tools we are developing are based on the instantiation of patterns. These patterns are designed on the basis of a classification of temporal requirements that we have established. The concepts of parallelism and hierarchy which characterize the Stocharts formalism compared to other state-transitions models help us build the foundations of our approach. An example of application to the control-command in the railway field is presented to illustrate the key concepts of our approach and its implementation.

Expressiveness of verifiable hierarchical clock systems

The modelling and analysis of multi-component discrete event systems is a challenging research area. Over 30 years, modelling and simulation research of discrete event system specification (DEVS) has been developed with (1) dense-time, (2) the I/O concept, and (3) hierarchical model construction. Nevertheless, DEVS model verification research began relatively recently considering the whole DEVS research history. In the meantime, over 15 years, the automata theory has been developed to cover the dense-time behaviour verification of discrete event systems. Especially, timed automata (TA) has performed the key role in the field. This paper builds on the research results that have been achieved from both theories of DEVS and TA. Thus contributions of this paper can be seen from each side. From the viewpoint of the DEVS theory, a finite and nondeterministic DEVS has been found as a verifiable class. From the viewpoint of the TA theory, a TA which is modular and hierarchical as well as verifiable, is proposed. To show the results, this paper uses the top down manner in which a general formalism is defined first and then its sub-classes are introduced.

Tools For Verification Of A Large Discrete System

Tools for modeling and verification of discrete event systems are implemented in Mathematica. The tools are based on binary decision diagrams (BDD) for which a Mathematica interface is provided. For modeling a compiler is developed translating a restricted class of Pascal into boolean expressions represented by BDDs. The tools are used in an application of a landing gear system of a fighter aircraft. This system is controlled by a software consisting of 1200 lines of Pascal. This code represented as a BDD is then analyzed using temporal logics. This article demonstrates the principle of the Pascal compiler.