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This paper addresses the problem of cyber-attack detection in a discrete event system by proposing a novel model. The model utilizes graph convolutional networks to extract spatial features from event sequences. Subsequently, it employs gated recurrent units to re-extract spatio-temporal features from these spatial features. The obtained spatio-temporal features are then fed into an attention model. This approach enables the model to learn the importance of different event sequences, ensuring that it is sufficiently general for identifying cyber-attacks, obviating the need to specify attack types. Compared with traditional methods that rely on synchronous product computations to synthesize diagnosers, our deep learning-based model circumvents state explosion problems. Our method facilitates real-time and efficient cyber-attack detection, eliminating the necessity to specifically identify system states or distinguish attack types, thereby significantly simplifying the diagnostic process. Additionally, we set an adjustable probability threshold to determine whether an event sequence has been compromised, allowing for customization to meet diverse requirements. Experimental results demonstrate that the proposed method performs well in cyber-attack detection, achieving over 99.9 % accuracy at a 1 % threshold and a weighted F1-score of 0.8126, validating its superior performance. [ABSTRACT FROM AUTHOR]

The supervisory control of Petri nets aims to enforce the undesired behavior as unreachable by designing a set of control places. This work presents a set cover approach to design maximally permissive supervisors. For each first-met bad marking, an integer linear programming problem is developed to obtain a control place to prohibit it. An objective function is formulated to make the maximal number of first-met bad markings forbidden. Then, we develop a set covering approach to minimize the number of selected control places. The proposed approach can guarantee the maximal permissiveness of the obtained supervisor and provide a trade-off between structural complexity and computational cost. Several examples are considered to validate the proposed method. [ABSTRACT FROM AUTHOR]

Industrial control systems (ICS) require system design and operation under cyber-attacks. This study aims to design a fallback control system that can switch from normal control to fallback control and verify its superiority. The target system is a factory automation (FA) system consisting of a normal programmable logic controller (PLC) and a fallback PLC. In this system, we design a fallback logic that takes over control in the case of cyber-attacks. The design of this logic requires a system model that manages smooth state transitions between normal control and fallback control in an integrated manner under cyber-attacks. In response, we model a control program in the framework of discrete event systems (DESs) and apply supervisory control to derive a supervisor model that can manage the system in an integrated manner. To ensure the controllability of the FA system during cyber-attacks, we design a control specification that includes a detection function to enable rapid switching of the control state. As a result, we generate the fallback logic from the supervisor model with guaranteed controllability under cyber-attacks and implement it in a fallback PLC to verify the effectiveness of the proposed logic. [ABSTRACT FROM AUTHOR]

Copyright of Automatisierungstechnik is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the realm of data protection strategies, differential privacy ensures that unauthorized entities cannot reconstruct original data from system outputs. This study explores discrete event systems, specifically through probabilistic automata. Central is the protection of state data, particularly the initial state privacy of multiple starting states. We introduce an evaluation criterion to safeguard initial states. Using advanced algorithms, the proposed method counters the probabilistic identification of any state within this collection by adversaries from observed data points. The efficacy is confirmed when the probability distributions of data observations tied to these states converge. If a system's architecture does not meet state differential privacy demands, we propose an enhanced supervisory control mechanism. This control upholds state differential privacy across all initial states, maintaining operational flexibility within the probabilistic automaton framework. Concluding, a numerical analysis validates the approach's strength in probabilistic automata and discrete event systems. [ABSTRACT FROM AUTHOR]

This paper presents an approach to solve the least-cost transition sequences estimation problem in labelled time Petri net (LTPN) systems with unobservable transitions. Particularly, the considered LTPN system is bounded, in which each transition has a nonnegative cost and is labelled as either observable or unobservable. We first introduce a graph, called a segmented modified state class graph (SMSCG), that is a compact representation of the partial state space of an LTPN system. Based on the SMSCG and an observed time-label sequence, a method to estimate logic consistent transition sequences is proposed. By exploiting the transitions-related timing constraints in SMSCGs, a procedure for determining which logic consistent transition sequences are timing consistent with the observed time-label sequence and a given time is reported. Finally, we develop an algorithm to perform the estimation of least-cost transition sequences. [ABSTRACT FROM AUTHOR]

This paper proposes a controller synthesis method based on matrix transformation and integer linear programming to address the problem of forbidden state controller design for Petri net systems with uncontrollable transitions. The key idea behind this method involves transforming generalized mutual exclusion constraints (GMEC) that represent the legal states of a Petri net system. Based on the incidence matrix of a Petri net, it divides the set of places into irrelevant places, uncontrollable places, and complementary places. By modifying the weights of complementary places and uncontrollable places in the given GMEC, it then converts the given GMEC into an allowable one by solving integer linear programming problems. Using the allowable GMEC, this paper designs a structural controller for Petri nets based on the principle of place invariants. Finally, it takes a part processing system as an example to show that the application is versatile and efficient, offering an effective solution for the controller design of intelligent manufacturing systems. [ABSTRACT FROM AUTHOR]

This paper considers the verification of decentralized fault pattern diagnosability for discrete event systems, where the pattern is modeled as a finite automaton whose accepted language is the objective to be diagnosed. We introduce a notion of codiagnosability to formalize the decentralized fault pattern diagnosability, which requires the pattern to be detected by one of the external local observers within a bounded delay. To this end, a structure, namely a verifier, is proposed to verify the codiagnosability of the system and the fault pattern. By studying an indeterminate cycle of the verifier, sufficient and necessary conditions are provided to test the codiagnosability. It is shown that the proposed method requires polynomial time at most. In addition, we present an approach to extend the proposed verifier structure so that it can be applied to centralized cases. [ABSTRACT FROM AUTHOR]

Information security is an important area of concern in modern computer-integrated systems. It involves implementing preventative measures to protect confidential data from potential vulnerabilities, such as unauthorized access, secret disclosure, modification, or destruction. Considering such threats, we investigate a particular confidentiality property called opacity, which specifies a system's ability to cover its 'secret' data from being interfered with by outside observers, termed as intruders. This paper discusses language-based opacity formulation and verification in the context of discrete event systems represented by partially observed Petri nets. In this context, we identify two opacity properties, called consistency and non-secrecy; then, we exploit the mathematical characterization of a net system, to separately check each property, by specifying two feasibility problems. The proposed method is carried out for two distinct settings of a system. The first setting is centralized, where an intruder is granted complete information about the system structure but a partial observation of its behavior. The second setting is decentralized, where a group of intruders cooperates to reveal the secret language, by using a coordinator. Finally, experimental findings are given, to demonstrate the proficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper investigated the verification of detectability for discrete event systems based on a class of partially observed unbounded Petri nets. In an unbounded net system, all transitions and partial places are assumed to be unobservable. The system administrator can only observe a few observable places, i.e., the number of tokens at these places can be observed, allowing for the estimation of current and subsequent states. The concepts of quasi-observable transitions, truly unobservable transitions, and partial markings are used to construct a basis coverability graph. According to this graph, four sufficient and necessary conditions of detectability are proposed. Correspondingly, a specific example is proposed to prove that the detectability can be verified in the unbounded net system. Furthermore, based on the conclusion of detectability, the system's ability to detect critical states was explored by using the basis coverability graph, called C-detectability. Two real-world examples are proposed to show that the detectability of discrete event systems has not only pioneered new research methods, but also demonstrated that the real conditions faced by this method are more general, and it has overcome the limitations of relying only on the ideal conditions of bounded systems for verification. [ABSTRACT FROM AUTHOR]

The diagnosability problem has been extensively studied over the past two decades for discrete event systems associated with intermittent faults. Diagnosability is a property that requires a large number of sensors for fault detection, which leads to expensive system deployment. To alleviate the above drawbacks, we propose a new property called intermittent fault manifestability, which is a weaker observation requirement for diagnosing the occurrence of intermittent faults. In order to verify the property, we consider fault events and their corresponding reset events and introduce two properties of f-manifestability and r-manifestability, respectively. Based on an intermittent fault pattern automaton, we first propose a diagnoser structure to track the occurrence of intermittent faults and prove that the verification of intermittent fault diagnosability can be transformed into the problem of detecting an intermittent fault language. Then, we present a pair verifier constructed by the strict composition of a fault diagnoser and a normal diagnoser, which are the subparts of the diagnoser with respect to the fault events and the normal events, respectively. Finally, we introduce necessary and sufficient conditions for verifying intermittent fault manifestability. [ABSTRACT FROM AUTHOR]

Cyber-physical systems are characterized by the intrinsic combination of software and physical components that usually include (wired and wireless) communication devices, sensors, actuators, and control processing units. Some wireless devices communicate over insecure channels, rendering cyber-physical systems at risk of malicious attacks that might lead to catastrophic damage. This paper touches upon the problem of sensor deception attacks in supervisory control of discrete-event systems, where an attacker can insert, delete, or replace sensor readings to mislead the supervisor and induce system damage. We model potential attacks using nondeterministic finite-state transducers and then introduce a new defence strategy that utilizes insertion functions. Insertion functions are a type of monitoring interface that alters the system's behaviour by adding extra observable events. Finally, we construct a nondeterministic finite-state transducer called a supervisor filter that recovers the original language generated by the plant by handling the altered language. The insertion function and the supervisor filter cooperate to control the system and confuse the intruder without confusing the supervisor. [ABSTRACT FROM AUTHOR]

Roughly speaking, differential privacy is a privacy-preserving strategy that guarantees attackers to be unlikely to infer, from the previous system output, the dataset from which an output is derived. This work introduces differential privacy to discrete event systems modeled by probabilistic automata to protect the state information pertaining to system resource configurations. State differential privacy is defined to protect the initial state of a discrete event system, which represents its initial resource configuration. Step-based state differential privacy verification is proposed in the framework of probabilistic automata, such that an attacker is unlikely to determine the initial state from which a system evolves, within a finite step of observations, if two systems with two different initial states satisfy state differential privacy. Specifically, the probability distributions of generating observations within a finite step from the two different initial states are approximate. If the two systems do not satisfy state differential privacy, a control specification is proposed, such that state differential privacy is enforced via supervisory control that is maximally permissive. Experimental studies are given to illustrate that the proposed method can effectively verify state differential privacy and enforce privacy protection in the probabilistic automata framework. [ABSTRACT FROM AUTHOR]

A new approach to the verification of current-state opacity for discrete event systems is proposed in this paper, which is modeled with unbounded Petri nets. The concept of opacity verification is first extended from bounded Petri nets to unbounded Petri nets. In this model, all transitions and partial places are assumed to be unobservable, i.e., only the number of tokens in the observable places can be measured. In this work, a novel basis coverability graph is constructed by using partial markings and quasi-observable transitions. By this graph, this research finds that an unbounded net system is current-state opaque if, for an arbitrary partial marking, there always exists at least one regular marking in the result of current-state estimation with respect to the partial marking not belonging to the given secret. Finally, a sufficient and necessary condition is proposed for the verification of current-state opacity. A manufacturing system example is presented to illustrate that the concept of current-state opacity can be verified for unbounded net systems. [ABSTRACT FROM AUTHOR]

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Control algorithms for programmable logic controllers are still developed based on the experience of those responsible for control in the industry. The IEC-61131-3 standard considers five programming languages: Ladder Diagram, Structured Text, Function Block Diagram, Instruction List, and Sequential Function Diagram, which use different function blocks to develop control algorithms. Within the control algorithms for discrete event systems, there are two types of blocks: those with discrete inputs and outputs, and those with discrete and analog inputs and discrete output. Of the latter, the present research shows the analysis and formal model of the blocks including the problems of accumulation of tokens and the restoration of the coils. This proposal includes logical blocks of timers, counters, positive and negative transition detectors and bistable elements, which, together with the AND, OR, AND-OR, contact lock, auto-loop and Set-Reset logics, can be modeled and analyzed control algorithms with a greater degree of complexity. This guarantees the safety of workers as well as machines. [ABSTRACT FROM AUTHOR]

This article aims to provide a perspective on the foundations and developments of the net unfolding techniques and their applications to discrete event systems. The numerous methods applied to concurrency presented in the literature can be roughly divided into two classes: those that assume concurrency can be represented by means of a non-deterministic form, and those that represent concurrency by means of causal relations. This study serves as an ideal starting point for researchers interested in true concurrency semantics by offering a concise literature review of one of the major streams of research towards concurrency and interleaving problems. In order to cope with the state-explosion problem, the unfolding approach is used. Based on the findings of concurrency theory, interleaving semantics are replaced with a unique partially ordered occurrence net. In this paper, we aim to provide a comprehensive review on the history of net unfoldings, the methods that are based on these unfoldings, and how they are used in discrete event systems for automatic verification and compact representations purposes. [ABSTRACT FROM AUTHOR]

Given a discrete event system, it is said to be opaque if an intruder who can partially observe system behavior cannot infer that the system is necessarily in a predefined secret. A discrete event system is current-state opaque if an intruder is never able to verify whether the current state of the system is within the secret states. This article addresses the verification of current-state opacity of a discrete event system modeled with Petri nets, where the secret is defined as a set of states. The existing methods cannot deal with large-sized systems due to the curse of dimensionality. Multi-valued decision diagrams (MDDs) are widely accepted as an efficient and compact data structure for representing the extremely large reachability sets of Petri nets. We show that MDDs can be used in Petri nets with partial observable transitions and propose an approach for the verification of current-state opacity for bounded Petri nets. It is shown by experimental studies that the symbolic approach is practically more efficient than traditional techniques such as basis reachability graphs (BRGs). [ABSTRACT FROM AUTHOR]

This paper addresses the fault diagnosis problem of PLC-based systems that can be modeled as Petri nets under a certain level of abstraction. The existing Petri-net-based fault diagnosis approaches often associate transitions and/or places with sensors and require that any change in sensor readings needs to be treated by a PLC, leading to a situation that the PLC would be too busy processing the changes in sensor readings to perform other tasks. This paper assumes that a PLC does not monitor the changes of readings of sensors all the time, but periodically reads the values of sensors when needed. The system output is defined as a marking sequence interleaved with possible observed transitions. A fault diagnosis algorithm is developed by defining and solving integer linear programing (ILP) problems whose size is regardless of the length of the system output. The proposed approach enjoys high computational efficiency compared with other ILP-based approaches and is more suitable for fault diagnosis of PLC-based systems with low computing power. [ABSTRACT FROM AUTHOR]

We propose a novel framework to generate recognizable scenes conditioned on natural language (NL) descriptions. The proposed modular approach decomposes the scene synthesis process into several manageable steps, in which it first infers a spatial layout of the desired scene from input descriptions by a spatial layout generator and generates the scene with a scene generator. Specifically, the proposed approach allows interactive tuning of the synthesized scene via NL, which helps to generate more complex and meaningful scenes, and to correct training errors or bias. We demonstrate the capability of the proposed approach on the challenging MS-COCO dataset and show that our approach can improve the quality of generated scenes, interpretability of the drawn scenes and semantic alignment to the input language descriptions. [ABSTRACT FROM AUTHOR]

The development of technologies is changing the traditional concept of teaching and learning in classrooms. In particular, information technology (IT) courses are rapidly adopting such changes as IT education's purpose is to cultivate students' capability to develop technologies by experiencing them in classrooms. In IT courses, deep learning has been used to improve teaching and learning ability through the use of sensing technology and related hardware/software. In teaching and learning, asynchronous, concurrent, and stochastic events occur because teachers and students have their protocols and behaviors in the related activities. Therefore, the design and teaching of courses should be based on a discrete event system that deals with discrete events. On the basis of this concept, we propose a deep learning model with the Petri net method to establish a logical modular system for IT course design and teaching. Because Petri nets are useful in simulation and analysis for the system modeling of asynchronous, concurrent, and stochastic events, we investigate how to use a Petri net to establish a deep learning model to develop and evaluate the curriculum of IT courses. The results of this study will contribute to building an efficient IT learning system that comprises sensing technology, information transmission, information processing, and feedback, which will require collaboration with pedagogical experts in the future. [ABSTRACT FROM AUTHOR]

Based on labeled time Petrinets (LTPN s), this paper proposed afault diagnosis method for discrete event systems with unobservable events. Firstly, by analyzing the deficiency of the modified state class graph (MSCG) of an LTPN system, this paper provided an improved MSCG. Secondly, it gave an observable label sequence and a time instant, it searched all the timing consistent paths by solving the linear programming problems associated with the paths in an improved MSCG, so as to analyze the systemfailure. Finally, it verified the effectiveness of the proposed method by taking the alternating bit protocol system as an example, which provided an effective scheme for the fault diagnosis of complex real-time systems. [ABSTRACT FROM AUTHOR]

In this paper, we focus on state estimation for constant-time labeled automata in a dense time context, i.e., the time constraints of the automata can be given according to real numbers. Given a sequence of timed observations (i.e., pairs of logical observations with their time stamps) collected from a system within a finite time window, a state estimation method is proposed to find the set of states in which the system might reside by the end of the time window. By using both labeling and timing information as well as the structure of the system, we can express any finite time evolution from one state to another into constraint satisfaction problems (CSPs). This structural analysis is independent of all collected sequences of timed observations and can be achieved offline, although its cost is exponential with respect to the number of states in the system. Consequently, two algorithms are designed to perform state estimation under a single observation and no observation, respectively, by solving a finite number of CSPs generated according to the system's structural information. Both algorithms can be jointly used in an iterative approach to perform state estimation for any sequence of timed observations. In such a case, the number of generated CSPs in the algorithms increases linearly with respect to the length of the observed sequence. [ABSTRACT FROM AUTHOR]

This paper proposes an iterative control policy to design a less restrictive and admissible Petri net (PN) controller for a Discrete Event System (DES) with uncontrollable transitions, when a maximally permissive controller is not obtains by. This paper exploits a structural supervisory control method, avoiding reachability graph. This exciting method addresses the controllability condition of the desired functioning PN to define it as General Mutual Exclusion constraints (GMEC), which leads to design place invariant-based controller. The controller is non-admissible if one control place is connected to uncontrollable transition. To obtain an admissible PN controller, if such a controller exists, authors propose constraints transformation, which is computationally complex, while the controller arcs displacement approach is unsystematic. Based on it, we develop the idea to iterate the structural supervisory control method, to ensure that control place is connected to controllable transition. Through this, it was found that the displacement of arcs is systematic and the controller is less restrictive and admissible, namely the supreme controller. The results indicate that the linear constraints are never violated through the firing of uncontrollable transitions. The finding of this work may serve to evaluate the structural optimality of the controller, in order to perform it practically. [ABSTRACT FROM AUTHOR]

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The paper concerns the design of a framework for implementing fault-tolerant control of hybrid assembly systems that connect human operators and fully automated technical systems. The main difficulty in such systems is related to delays that result from objective factors influencing human operators' work, e.g., fatigue, experience, etc. As the battery assembly system can be considered a firm real-time one, these delays are treated as faults. The presented approach guarantees realtime compensation of delays, and the fully automated part of the system is responsible for this compensation. The paper begins with a detailed description of a battery assembly system in which two cooperating parts can be distinguished: fully automatic and semi-automatic. The latter, nonderministic in nature, is the main focus of this paper. To describe and analyze the states of the battery assembly system, instead of the most commonly used simulation, the classic max-plus algebra with an extension allowing one to express non-deterministic human operators' work is used. In order to synchronize tasks and schedule (according to the reference schedule) automated and human operators' tasks, it is proposed to use a wireless IoT platform called KIS.ME. As a result, it allows a reference model of human performance to be defined using fuzzy logic. Having such a model, predictive delays tolerant planning is proposed. The final part of the paper presents the achieved results, which clearly indicate the potential benefits that can be obtained by combining the wireless KIS.ME architecture (allocated in the semi-automatic part of the system) with wired standard production networks. [ABSTRACT FROM AUTHOR]

This paper presents an approach to automatically amend an erroneous model of an implementation using a safety specification as the basis to ensure safety. Industrially, safety PLCs are common to ensure safe operations. However, before its commissioning, the implemented safety code must be tested for faults caused by spurious transitions and missing safety transitions. Spurious transitions are implemented events that are not prescribed by the safety specification, while missing safety transitions are unimplemented safety events that are prescribed by the safety specification. The presence of these faults can result in material or human damage. The proposed approach requires the model of an implementation to be trace equivalent with the given safety specification only in terms of traces composed of safety events, which is captured by the notion of safe-IOCOS. If the implementation emits other than the specified safety events then the implementation is not safe-IOCOS and requires amendment. This is achieved by removing the spurious transitions and adding the missing safety events in the implementation using synthesis techniques from the supervisory control theory. The infimal controllable superlanguage is used to compute the infimal safety extension , which adds the missing safety transitions. It is shown how the resulting model of an implementation after amendment is both safe-IOCOS and controllable with respect to the specification. [ABSTRACT FROM AUTHOR]

This study considers the synchronisation of events modelled by graphs of timed event systems. The start and finish points of events are indicated by the firing of transitions in the system. Synchronising the firing of these transitions control events, which are activities within a manufacturing system. Synchronisation is achieved by controlling the inflow of raw materials into the system. A feedback controller is proposed to control the flow of incoming feedstock. The controller parameters are calculated. Delays are applied to the input supply and the production rate is established when the control of the synchronisation constraints is satisfied. The proposed method ensures that the system control operates according to the control strategy of ‘just-in-time’ production planning. [ABSTRACT FROM AUTHOR]

Privacy protection has received widespread attention from the community of discrete event systems to protect the sensitive information of users or organizations from being leaked. The existing privacy protection methods cannot protect the state information of probabilistic discrete event systems via repeated observations, which represents the information pertaining to system resource configurations. This work introduces differential privacy into the framework of probabilistic labeled Petri nets to solve the problems pertaining to the initial state protection. For two initial states that are adjacent under a specified measure, a state differential privacy verification method is proposed by determining whether the probability distributions of observations generated from adjacent initial states are similar. An external attacker is unlikely to infer the initial state via repeated observations if the system satisfies state differential privacy for certain adjacent initial states. For a probabilistic labeled Petri net, which does not satisfy state differential privacy, a supervisory control method is proposed for enforcement. A maximally permissive controller can be constructed based on the control specification proposed in this paper. Experimental studies show that the method proposed in the paper can effectively protect the privacy of given adjacent initial states. • Differential privacy is introduced into DESs to protect the secret. • Define state differential privacy to analyze whether the secret is protected. • Verify adjacent initial state-based differential privacy in probabilistic DESs. • A maximally permissive controller is constructed for privacy enforcement. [ABSTRACT FROM AUTHOR]

This paper addresses the state estimation of timed discrete event systems, where the occurrence of an event is associated with a time delay and the initial state of the system belongs to a set of possible initial states. A discrete event system is modeled with a bounded timed labeled Petri net whose unobservable subnet is acyclic, and the behavior of the system under a global time clock can be observed. The procedure for state estimations of partially observed Petri nets is refined by the introduction of time in discrete event systems. We apply the symbolic techniques to the representation of states and transition relations of bounded timed labeled Petri nets. Then we propose an online algorithm for the computation of state estimations generated by timed observations. [ABSTRACT FROM AUTHOR]

Copyright of Control Theory & Applications / Kongzhi Lilun Yu Yinyong is the property of Editorial Department of Control Theory & Applications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper formulates a new control problem of achieving the global objective of a discrete event system with networked control agents that pursue only their own objectives and compete with each other. In this framework, each agent makes a decision to meet its own private objective with a given mask during state observation of the system and such a decision can be changed by the influence of other agents connected through a directed network. Agents with an initial decision of enabling or disabling of an event do not change their decision, but those agents reserving their decision in an undetermined way can change their decision to either enabling or disabling depending on the influence from other agents. We derive a condition for convergence of the decision of all agents. Based on the individual decision of each agent, the final decision for enabling or disabling of an event is made by majority rule. We present the network-controllability of a global objective with respect to a given mask set as a main condition with which the networked agents can meet the global objective while they pursue only their own private objectives. [ABSTRACT FROM AUTHOR]

• Attacks on industrial control system can degrade security of the system and the environment, decrease the quality of the product and damage equipment. • The S.A.F.E. (Security approach based on filter execution) approach detects malicious orders emitted from the control part to physical system. • Generic methodology based on three steps allows generating a filter based on behavioral modeling (DES) with sequential and temporal constraints. • Indicators (distance, trajectory, time, over-soliciting) specifically created for detecting direct or indirect attacks that can occur between levels 1 and 0 allow executing detection mechanisms to characterize abnormal orders. • The S.A.F.E. approach proposed a physical implementation on the ICS architecture as close as possible to the operative part in order to reduce the attack surface. Since the beginning of the 21th century, Industrial Control Systems (ICS) have been targeted by hackers. The main motives for the interest to ICS is the ease for performing cyberattacks and the potential damages inflicted to the system and its environment in case of success. The purpose of this paper is to propose an approach for detecting malicious orders in discrete-event system. Four types of attacks (direct, sequential, temporal and over-soliciting) that affect an industrial system are studied in this work. Based on the vulnerabilities in ICS and the positioning of other techniques, an innovative methodology is exposed in this paper to develop detection mechanisms based on the "automation-knowledge". Thus, by using models of system with an improved notion of distance and trajectory, our filters based approach provides good results for detecting cyberattacks in lower levels of ICS architecture by analyzing the malicious nature of the orders sent. Different types of detection mechanisms based on the concept of distance and trajectory are detailed in this study. We also provide results on simulation examples and an industrial platform. To conclude, improvements of our approach are discussed. [ABSTRACT FROM AUTHOR]

This paper focuses on the algebraic expression of discrete event systems (DES), which bridges the gap between linear control system theory and discrete event system theory. For this purpose, we firstly give an overview of different approaches towards an algebraic description existing in the literature in the area of different classes of DES, such as Petri nets, automata and Boolean networks. After that, the complexity, applicability for control and the structural restrictions are compared. Finally, possible future developments are highlighted. [ABSTRACT FROM AUTHOR]

Abstract It has been argued for some time now, based on classroom, textbook and practical examples that the size of verifiers and diagnosers is comparable. This belief has been corroborated by a recent paper, where it is conjectured, based on a rigorous statistical analysis, that the size of the states of diagnosers is Θ (n 0. 77 log k + 0. 63) , on the average, where k (resp. n) is the number of events (resp. states) of the plant automaton. However, there is another difficulty that hampers the use of diagnosers in diagnosability verification: the search for cycle, which has been proved to be factorial. We present, in this paper, a necessary and sufficient condition for a language codiagnosability of DES and, based on this condition, we propose a new test for its verification that is based on a diagnoser-like automaton that has following advantages: (i) the diagnosability verification test is based on the search for strongly connected components, which is linear in the state size; (ii) it has both observable and unobservable events of the plant in its event set, and so the usual assumptions on language liveness and nonexistence of unobservable cycles of states connected with unobservable events only are no longer required, and; (iii) T-codiagnosability can be computed by adding weights associated with transitions of the plant automaton, and, as a consequence K-codiagnosability, since it is a particular case of T-codiagnosability when all weights are set equal to 1. [ABSTRACT FROM AUTHOR]