Determinacy and Decidability of Reachability Games with Partial Observation on Both Sides

We prove two determinacy and decidability results about two-players stochastic reachability games with partial observation on both sides and finitely many states, signals and actions

History-Deterministic Timed Automata

International audienceWe explore the notion of history-determinism in the context of timed automata (TA). Historydeterministic automata are those in which nondeterminism can be resolved on the fly, based on the run constructed thus far. History-determinism is a robust property that admits different game-based characterisations, and history-deterministic specifications allow for game-based verification without an expensive determinization step. We show yet another characterisation of history-determinism in terms of fair simulation, at the general level of labelled transition systems: a system is history-deterministic precisely if and only if it fairly simulates all language smaller systems. For timed automata over infinite timed words it is known that universality is undecidable for Büchi TA. We show that for history-deterministic TA with arbitrary parity acceptance, timed universality, inclusion, and synthesis all remain decidable and are ExpTime-complete. For the subclass of TA with safety or reachability acceptance, we show that checking whether such an automaton is history-deterministic is decidable (in ExpTime), and history-deterministic TA with safety acceptance are effectively determinizable without introducing new automata states

Qualitative Reachability in Stochastic BPA Games

We consider a class of infinite-state stochastic games generated by stateless pushdown automata (or, equivalently, 1-exit recursive state machines), where the winning objective is specified by a regular set of target configurations and a qualitative probability constraint `>0' or `=1'. The goal of one player is to maximize the probability of reaching the target set so that the constraint is satisfied, while the other player aims at the opposite. We show that the winner in such games can be determined in PTIME for the `>0' constraint, and both in NP and coNP for the `=1' constraint. Further, we prove that the winning regions for both players are regular, and we design algorithms which compute the associated finite-state automata. Finally, we show that winning strategies can be synthesized effectively.Comment: Submitted to Information and Computation. 48 pages, 3 figure

Competitive optimisation on timed automata

Timed automata are finite automata accompanied by a finite set of real-valued variables called clocks. Optimisation problems on timed automata are fundamental to the verification of properties of real-time systems modelled as timed automata, while the control-program synthesis problem of such systems can be modelled as a two-player game. This thesis presents a study of optimisation problems and two-player games on timed automata under a general heading of competitive optimisation on timed automata. This thesis views competitive optimisation on timed automata as a multi-stage decision process, where one or two players are confronted with the problem of choosing a sequence of timed moves—a time delay and an action—in order to optimise their objectives. A solution of such problems consists of the “optimal” value of the objective and an “optimal” strategy for each player. This thesis introduces a novel class of strategies, called boundary strategies, that suggest to a player a symbolic timed move of the form (b, c, a)— “wait until the value of the clock c is in very close proximity of the integer b, and then execute a transition labelled with the action a”. A distinctive feature of the competitive optimisation problems discussed in this thesis is the existence of optimal boundary strategies. Surprisingly perhaps, many competitive optimisation problems on timed automata of practical interest admit optimal boundary strategies. For example, optimisation problems with reachability price, discounted price, and average-price objectives, and two-player turn-based games with reachability time and average time objectives. The existence of optimal boundary strategies allows one to work with a novel abstraction of timed automata, called a boundary region graph, where players can use only boundary strategies. An interesting property of a boundary region graph is that, for every state, the set of reachable states is finite. Hence, the existence of optimal boundary strategies permits us to reduce competitive optimisation problem on a timed automaton to the corresponding competitive optimisation problem on a finite graph

Le problème de la valeur dans les jeux stochastiques

La théorie des jeux est un outils standard quand il s'agit de l'étude des systèmes réactifs. Ceci est une conséquence de la variété des modèle de jeux tant au niveau de l'interaction des joueurs qu'au niveau de l'information que chaque joueur possède.Dans cette thèse, on étudie le problème de la valeur pour des jeux où les joueurs possèdent une information parfaite, information partiel et aucune information. Dans le cas où les joueurs possèdent une information parfaite sur l'état du jeu,on étudie le problème de la valeur pour des jeux dont les objectifs sont des combinaisons booléennes d'objectifs qualitatifs et quantitatifs.Pour les jeux stochastiques à un joueur, on montre que les valeurs sont calculables en temps polynomiale et on montre que les stratégies optimalespeuvent être implementées avec une mémoire finie.On montre aussi que notre construction pour la conjonction de parité et de la moyenne positivepeut être étendue au cadre des jeux stochastiques à deux joueurs. Dans le cas où les joueurs ont une information partielle,on étudie le problème de la valeur pour la condition d'accessibilité.On montre que le calcul de l'ensemble des états à valeur 1 est un problème indécidable,on introduit une sous classe pour laquelle ce problème est décidable.Le problème de la valeur 1 pour cette sous classe est PSPACE-complet dansle cas de joueur aveugle et dans EXPTIME dans le cas de joueur avec observations partielles.Game theory proved to be very useful in the fieldof verification of open reactive systems. This is due to the widevariety of games' model that differ in the way players interactand the amount of information players have.In this thesis, we study the value problem forgames where players have full knowledge on their current configurationof the game, partial knowledge, and no knowledge.\\In the case where players have perfect information,we study the value problem for objectives that consist in combinationof qualitative and quantitative conditions.In the case of one player stochastic games, we show thatthe values are computable in polynomial time and show thatthe optimal strategies exist and can be implemented with finite memory.We also showed that our construction for parity and positive-average Markov decisionprocesses extends to the case of two-player stochastic games.\\In the case where the players have partial information,we study the value problem for reachability objectives.We show that computing the set of states with value 1 is an undecidableproblem and introduce a decidable subclass for the value 1 problem.This sub class is PSPACE-complete in the case of blind controllersand EXPTIME is the setting of games with partial observations.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Playing with Trees and Logic

This document proposes an overview of my research sinc

Competative optimisation on timed automata

Timed automata are finite automata accompanied by a finite set of real-valued variables called clocks. Optimisation problems on timed automata are fundamental to the verification of properties of real-time systems modelled as timed automata, while the control-program synthesis problem of such systems can be modelled as a two-player game. This thesis presents a study of optimisation problems and two-player games on timed automata under a general heading of competitive optimisation on timed automata. This thesis views competitive optimisation on timed automata as a multi-stage decision process, where one or two players are confronted with the problem of choosing a sequence of timed moves—a time delay and an action—in order to optimise their objectives. A solution of such problems consists of the “optimal” value of the objective and an “optimal” strategy for each player. This thesis introduces a novel class of strategies, called boundary strategies, that suggest to a player a symbolic timed move of the form (b, c, a)— “wait until the value of the clock c is in very close proximity of the integer b, and then execute a transition labelled with the action a”. A distinctive feature of the competitive optimisation problems discussed in this thesis is the existence of optimal boundary strategies. Surprisingly perhaps, many competitive optimisation problems on timed automata of practical interest admit optimal boundary strategies. For example, optimisation problems with reachability price, discounted price, and average-price objectives, and two-player turn-based games with reachability time and average time objectives. The existence of optimal boundary strategies allows one to work with a novel abstraction of timed automata, called a boundary region graph, where players can use only boundary strategies. An interesting property of a boundary region graph is that, for every state, the set of reachable states is finite. Hence, the existence of optimal boundary strategies permits us to reduce competitive optimisation problem on a timed automaton to the corresponding competitive optimisation problem on a finite graph.EThOS - Electronic Theses Online ServiceGBUnited Kingdo