134 research outputs found
A survey on compositional algorithms for verification and synthesis in supervisory control
This survey gives an overview of the current research on compositional algorithms for verification and synthesis of modular systems modelled as interacting finite-state machines. Compositional algorithms operate by repeatedly simplifying individual components of a large system, replacing them by smaller so-called abstractions, while preserving critical properties. In this way, the exponential growth of the state space can be limited, making it possible to analyse much bigger state spaces than possible by standard state space exploration. This paper gives an introduction to the principles underlying compositional methods, followed by a survey of algorithmic solutions from the recent literature that use compositional methods to analyse systems automatically. The focus is on applications in supervisory control of discrete event systems, particularly on methods that verify critical properties or synthesise controllable and nonblocking supervisors
Exploration policies for on-the-fly controller synthesis: a reinforcement learning approach
Controller synthesis is in essence a case of model-based planning for non-deterministic environments in which plans (actually âstrategiesâ) are meant to preserve system goals indefinitely. In the case of supervisory control environments are specified as the parallel composition of state machines and valid strategies are required to be ânon-blockingâ (i.e., always enabling the environment to reach certain marked states) in addition to safe (i.e., keep the system within a safe zone). Recently, On-the-fly Directed Controller Synthesis techniques were proposed to avoid the exploration of the entire -and exponentially large- environment space, at the cost of non-maximal permissiveness, to either find a strategy or conclude that there is none. The incremental exploration of the plant is currently guided by a domain-independent human-designed heuristic. In this work, we propose a new method for obtaining heuristics based on Reinforcement Learning (RL). The synthesis algorithm is thus framed as an RL task with an unbounded action space and a modified version of DQN is used. With a simple and general set of features that abstracts both states and actions, we show that it is possible to learn heuristics on small versions of a problem that generalize to the larger instances, effectively doing zero-shot policy transfer. Our agents learn from scratch in a highly partially observable RL task and outperform the existing heuristic overall, in instances unseen during training
A Forward On-The-Fly Approach for Safety and Reachability Controller Synthesis of Timed Systems
RĂSUMĂ
Cette thĂšse sâintĂ©resse Ă la synthĂšse de contrĂŽleurs pour des systĂšmes temps rĂ©el (systĂšmes temporisĂ©s). Partant dâun systĂšme temps rĂ©el modĂ©lisĂ© par un rĂ©seau de Petri temporel composĂ© de transitions contrĂŽlables et non contrĂŽlables (TPN), le contrĂŽle vise Ă forcer, en restreignant les intervalles de franchissement des transitions contrĂŽlables, le systĂšme Ă satisfaire les propriĂ©tĂ©s souhaitĂ©es.
Nous proposons, dans cette thĂšse, un algorithme pour synthĂ©tiser de tels contrĂŽleurs pour des propriĂ©tĂ©s de sĂ»retĂ© et dâaccessibilitĂ©. Cet algorithme, basĂ© sur la mĂ©thode de graphe de classes dâĂ©tats, calcule Ă la volĂ©e les classes dâĂ©tats atteignables du TPN tout en collectant progressivement les sous-intervalles de tir Ă Ă©viter, afin de satisfaire les propriĂ©tĂ©s souhaitĂ©es. Avec cet algorithme, il nâest plus nĂ©cessaire de calculer les prĂ©dĂ©cesseurs contrĂŽlables et de partitionner rĂ©cursivement les classes dâĂ©tats jusquâĂ atteindre un point fixe, comme câest le cas dans les autres approches basĂ©es sur lâexploration, en avant et en arriĂšre, de lâespace des Ă©tats du systĂšme. Nous prouvons formellement la correction de lâalgorithme, puis nous montrons que dans la catĂ©gorie des contrĂŽleurs basĂ©s sur la restriction des intervalles de tir, lâalgorithme, proposĂ© dans cette thĂšse, synthĂ©tise un contrĂŽleur optimal (le plus permissif possible).
Afin dâattĂ©nuer davantage le problĂšme dâexplosion combinatoire, nous montrons comment combiner cette approche avec une abstraction par lâinclusion, par union-convexe ou par enveloppe-convexe. Nous montrons Ă©galement comment exploiter cet algorithme pour gĂ©nĂ©rer des contrĂŽleurs dĂ©centralisĂ©s.
Enfin, nous proposons dâappliquer cet algorithme pour contrĂŽler des TPN par des chronomĂštres. Notre algorithme permet de partitionner les intervalles des transitions en âbonsâ et âmauvaisâ sous-intervalles (Ă Ă©viter). LâidĂ©e est dâutiliser des chronomĂštres pour suspendre les tĂąches (transitions) durant leurs mauvais sous-intervalles et les activer dans leurs âbons sous-intervallesâ. Il sâagit donc de contrĂŽler les rĂ©seaux de Petri temporels en associant des chronomĂštres aux transitions contrĂŽlables, pour obtenir ainsi des rĂ©seaux de Petri temporels contrĂŽlĂ©s.----------ABSTRACT
This thesis deals with controller synthesis for real time systems (timed systems). Given a real time system modeled as a Time Petri Net (TPN) with controllable and uncontrollable transitions, the control aims at forcing the system to satisfy properties of interest, by limiting the firing intervals of controllable transitions. We propose, in this thesis, an algorithm to synthesize such controllers for safety / reachability properties.
This algorithm, based on the state class graph method, computes on-the-fly the reachable state classes of the TPN while collecting progressively firing subintervals to be avoided so that the property is satisfied. It does not need to compute controllable predecessors and then split state classes until reaching a fixpoint, as it is the case for other approaches based on backward and forward exploration of state space of the system. We prove formally the correctness of the algorithm and show that, in the category of state dependent controllers based on the restriction of firing intervals, the algorithm proposed in this thesis, synthesizes maximally permissive controllers.
In order to attenuate the state explosion problem, we show how to combine efficiently this approach with an abstraction by inclusion, convex union or convex hull. Afterwards, we discuss the compatibility of this method with distributed systems and decentralized controllers.
Finally, we apply this algorithm to control TPN with controllable and uncontrollable transitions by stopwatch. In this approach, we find the subintervals violating the given properties and our objective is to suspend the tasks (transitions) during their bad subintervals and to resume them later. The controller is synthesized through the same algorithm already introduced. In this approach, we suggest to control time Petri nets by associating stopwatches to controllable transitions and to achieve a controlled time Petri nets
Principles of Security and Trust
This open access book constitutes the proceedings of the 8th International Conference on Principles of Security and Trust, POST 2019, which took place in Prague, Czech Republic, in April 2019, held as part of the European Joint Conference on Theory and Practice of Software, ETAPS 2019. The 10 papers presented in this volume were carefully reviewed and selected from 27 submissions. They deal with theoretical and foundational aspects of security and trust, including on new theoretical results, practical applications of existing foundational ideas, and innovative approaches stimulated by pressing practical problems
Formal Techniques for Component-based Design of Embedded Systems
Embedded systems have become ubiquitous - from avionics and automotive over consumer electronics to medical devices. Failures may entailmaterial damage or compromise safety of human beings. At the same time, shorter product cycles, together with fast growing complexity of the systems to be designed, create a tremendous need for rigorous design techniques. The goal of component-based construction is to build complex systems from simpler components that are well understood and can be (re)used so as to accelerate the design process. This document presents a summary of the formal techniques for component-based design of embedded systems I have (co-)developed
Contagion aÌ effet de seuil dans les reÌseaux complexes
Networks arise frequently in the study of complex systems, since interactions among the components of such systems are critical. Networks can act as a substrate for dynamical process, such as the diffusion of information or disease throughout populations. Network structure can determine the temporal evolution of a dynamical process, including the characteristics of the steady state.The simplest representation of a complex system is an undirected, unweighted, single layer graph. In contrast, real systems exhibit heterogeneity of interaction strength and type. Such systems are frequently represented as weighted multiplex networks, and in this work we incorporate these heterogeneities into a master equation formalism in order to study their effects on spreading processes. We also carry out simulations on synthetic and empirical networks, and show that spreading dynamics, in particular the speed at which contagion spreads via threshold mechanisms, depend non-trivially on these heterogeneities. Further, we show that an important family of networks undergo reentrant phase transitions in the size and frequency of global cascades as a result of these interactions.A challenging feature of real systems is their tendency to evolve over time, since the changing structure of the underlying network is critical to the behaviour of overlying dynamical processes. We show that one aspect of temporality, the observed âburstinessâ in interaction patterns, leads to non-monotic changes in the spreading time of threshold driven contagion processes.The above results shed light on the effects of various network heterogeneities, with respect to dynamical processes that evolve on these networks.Les interactions entre les composants des systeÌmes complexes font eÌmerger diffeÌrents types de reÌseaux. Ces reÌseaux peuvent jouer le roÌle dâun substrat pour des processus dynamiques tels que la diffusion dâinformations ou de maladies dans des populations. Les structures de ces reÌseaux deÌterminent lâeÌvolution dâun processus dynamique, en particulier son reÌgime transitoire, mais aussi les caracteÌristiques du reÌgime permanent.Les systeÌmes complexes reÌels manifestent des inteÌractions heÌteÌrogeÌnes en type et en intensiteÌ. Ces systeÌmes sont repreÌseteÌs comme des reÌseaux pondeÌreÌs aÌ plusieurs couches. Dans cette theÌse, nous deÌveloppons une eÌquation maiÌtresse afin dâinteÌgrer ces heÌteÌrogeÌneÌiteÌs et dâeÌtudier leurs effets sur les processus de diffusion. AÌ lâaide de simulations mettant en jeu des reÌseaux reÌels et geÌneÌreÌs, nous montrons que les dynamiques de diffusion sont lieÌes de manieÌre non triviale aÌ lâheÌteÌrogeÌneÌiteÌ de ces reÌseaux, en particulier la vitesse de propagation dâune contagion baseÌe sur un effet de seuil. De plus, nous montrons que certaines classes de reÌseaux sont soumises aÌ des transitions de phase reÌentrantes fonctions de la taille des âglobal cascadesâ.La tendance des reÌseaux reÌels aÌ eÌvoluer dans le temps rend difficile la modeÌlisation des processus de diffusion. Nous montrons enfin que la dureÌe de diffusion dâun processus de contagion baseÌ sur un effet de seuil change de manieÌre non-monotone du fait de la preÌsence deârafalesâ dans les motifs dâinteÌractions. Lâensemble de ces reÌsultats mettent en lumieÌre les effets de lâheÌteÌrogeÌneÌiteÌ des reÌseaux vis-aÌ-vis des processus dynamiques y eÌvoluant
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