Synthesizing Distinguishing Formulae for Real Time Systems

This paper describes a technique for generating diagnostic information for the timed bisimulation equivalence and the timed simulation preorder. More precisely, given two (parallel) networks of regular real-time processes, the technique will provide a logical formula that differentiates them in case they are not timed (bi)similar. Our method may be seen as an extension of the algorithm by Cerans for deciding timed bisimilarity in that information of time-quantities has been added sufficient for generating distinguishing formulae. The technique has been added to the automatic verification tool EPSILON and applied to various examples

Utilization of timed automata as a verification tool for real-time security protocols

Thesis (Master)--Izmir Institute of Technology, Computer Engineering, Izmir, 2010Includes bibliographical references (leaves: 85-92)Text in English; Abstract: Turkish and Englishxi, 92 leavesTimed Automata is an extension to the automata-theoretic approach to the modeling of real time systems that introduces time into the classical automata. Since it has been first proposed by Alur and Dill in the early nineties, it has become an important research area and been widely studied in both the context of formal languages and modeling and verification of real time systems. Timed automata use dense time modeling, allowing efficient model checking of time-sensitive systems whose correct functioning depend on the timing properties. One of these application areas is the verification of security protocols. This thesis aims to study the timed automata model and utilize it as a verification tool for security protocols. As a case study, the Neuman-Stubblebine Repeated Authentication Protocol is modeled and verified employing the time-sensitive properties in the model. The flaws of the protocol are analyzed and it is commented on the benefits and challenges of the model

Automata and Logics for Concurrent Systems: Realizability and Verification

Automata are a popular tool to make computer systems accessible to formal methods. While classical finite automata are suitable to model sequential boolean programs, models of concurrent systems involve several interacting processes and extend finite-state machines in various respects. This habilitation thesis surveys several such extensions, including pushdown automata with multiple stacks, communicating automata with fixed, parameterized, or dynamic communication topology, and automata running on words over infinite alphabets. We focus on two major questions of classical automata theory, namely realizability (asking whether a specification has an automata counterpart) and model checking (asking whether a given automaton satisfies its specification)

Sémantique compositionnelle et raffinement de systèmes temporisés : application aux automates temporisés d'UPPAAL et au langage FIACRE

Les systèmes temps-réel sont massivement impliqués dans de nombreuses applications, dont notre vie dépend comme les logiciels embarqués dans les voitures et les avions. Pour ces systèmes des erreurs inattendues ne sont pas acceptables. De ce fait, assurer la correction de ces systèmes est une tâche primordiale. Les systèmes temps-réel représentent un large spectre de systèmes automatisés dont la correction dépend de la ponctualité des événements (timeliness) et pas seulement de leurs propriétés fonctionnelles. Chaque événement doit être produit selon la date indiquée par la spécification du système. Les systèmes temps-réel sont concurrents et embarqués, et conçus comme un assemblage de composants en interaction. Malgré les progrès réalisés dans les techniques de model checking, la vérification et l'analyse des systèmes temps-réel représentent toujours un défi autant pour les chercheurs que les praticiens. Pour étudier le comportement des systèmes temps-réel, différents formalismes ont été considérés comme les automates temporisés, les réseaux de Petri temporisés et les algèbres de processus. Cela donne lieu à plusieurs points délicats concernant le raffinement, la composition et la vérification. Ces points représentent un champ de recherche intensif. Ma thèse présente une étude des systèmes temps-réel focalisée sur les notions de sémantique, de composition et de raffinement. Elle décrit nos efforts pour explorer et étendre les formalismes temps-réel. Nous avons abordé les concepts de base de la modélisation des systèmes temps réel tels que les variables partagées, la communication, les priorités, la dynamicité, etc. La contribution de cette thèse porte sur la définition d’un cadre formel pour raisonner sur la sémantique, la composition et le raffinement des systèmes temporisés. Nous avons instancié ce cadre pour le formalisme des automates temporisés et le langage Fiacre.Nowadays, real-time systems are intensively involved in many applications on which our life is dependent, like embedded software in cars and planes. For these systems unexpected errors are not acceptable. Real-time systems represent a large spectrum of automated systems of which correctness depends on the timing of events (timeliness) and not only on their functional properties. Each event must be produced on time. Realtime systems can be concurrent and embedded where different interactive modules and components are assembled together. Despite advances in model checking techniques, the verification and analysis of real-time systems still represent a strong challenge for researchers and practitioners. To study the behavior of real-time systems, different formalisms have been considered like timed automata, time Petri nets and timed algebra, and several challenges concerning refinement, composition and verification have emerged. These points represent an intensive field of research. This thesis describes our effort to explore and extend real-time formalisms. We have revisited real-time language semantics, focusing on composition and refinement. We have addressed high level concepts like shared variables, communication, priorities, dynamicity, etc. The main contribution consists of a theoretical study of timed systems where we establish a framework for reasoning on composition, refinement and semantics. We instantiate this framework for timed automata and the Fiacre language

Model-Based Verification, Optimization, Synthesis and Performance Evaluation of Real-Time Systems

International audienceThis article aims at providing a concise and precise Travellers Guide, Phrase Book or Reference Manual to the timed automata modeling formalism introduced by Alur and Dill [8, 9]. The paper gives comprehensive definitions of timed automata, priced (or weighted) timed automata, and timed games and highlights a number of results on associated decision problems related to model checking, equivalence checking, optimal scheduling, the existence of winning strategies, and then statistical model checking

From computability to executability : a process-theoretic view on automata theory

The theory of automata and formal language was devised in the 1930s to provide models for and to reason about computation. Here we mean by computation a procedure that transforms input into output, which was the sole mode of operation of computers at the time. Nowadays, computers are systems that interact with us and also each other; they are non-deterministic, reactive systems. Concurrency theory, split off from classical automata theory a few decades ago, provides a model of computation similar to the model given by the theory of automata and formal language, but focuses on concurrent, reactive and interactive systems. This thesis investigates the integration of the two theories, exposing the differences and similarities between them. Where automata and formal language theory focuses on computations and languages, concurrency theory focuses on behaviour. To achieve integration, we look for process-theoretic analogies of classic results from automata theory. The most prominent difference is that we use an interpretation of automata as labelled transition systems modulo (divergence-preserving) branching bisimilarity instead of treating automata as language acceptors. We also consider similarities such as grammars as recursive specifications and finite automata as labelled finite transition systems. We investigate whether the classical results still hold and, if not, what extra conditions are sufficient to make them hold. We especially look into three levels of Chomsky's hierarchy: we study the notions of finite-state systems, pushdown systems, and computable systems. Additionally we investigate the notion of parallel pushdown systems. For each class we define the central notion of automaton and its behaviour by associating a transition system with it. Then we introduce a suitable specification language and investigate the correspondence with the respective automaton (via its associated transition system). Because we not only want to study interaction with the environment, but also the interaction within the automaton, we make it explicit by means of communicating parallel components: one component representing the finite control of the automaton and one component representing the memory. First, we study finite-state systems by reinvestigating the relation between finite-state automata, left- and right-linear grammars, and regular expressions, but now up to (divergence-preserving) branching bisimilarity. For pushdown systems we augment the finite-state systems with stack memory to obtain the pushdown automata and consider different termination styles: termination on empty stack, on final state, and on final state and empty stack. Unlike for language equivalence, up to (divergence-preserving) branching bisimilarity the associated transition systems for the different termination styles fall into different classes. We obtain (under some restrictions) the correspondence between context-free grammars and pushdown automata for termination on final state and empty stack. We show how for contrasimulation, a weaker equivalence than branching bisimilarity, we can obtain the correspondence result without some of the restrictions. Finally, we make the interaction within a pushdown automaton explicit, but in a different way depending on the termination style. By analogy of pushdown systems we investigate the parallel pushdown systems, obtained by augmenting finite-state systems with bag memory, and consider analogous termination styles. We investigate the correspondence between context-free grammars that use parallel composition instead of sequential composition and parallel pushdown automata. While the correspondence itself is rather tight, it unfortunately only covers a small subset of the parallel pushdown automata, i.e. the single-state parallel pushdown automata. When making the interaction within parallel pushdown automata explicit, we obtain a rather uniform result for all termination styles. Finally, we study computable systems and the relation with exective and computable transition systems and Turing machines. For this we present the reactive Turing machine, a classical Turing machine augmented with capabilities for interaction. Again, we make the interaction in the reactive Turing machine between its finite control and the tape memory explicit

Time At Your Service: Schedulability Analysis of Real-Time and Distributed Services

The software today is distributed over several processing units. At a large scale this may span over the globe via the internet, or at the micro scale, a software may be distributed on several small processing units embedded in one device. Real-time distributed software and services need to be timely and respond to the requests in time. The Quality of Service of real time software depends on how it schedules its tasks to be executed. The state of the art in programming distributed software, like in Java, the scheduling is left to the underlying infrastructure and in particular the operating system, which is not anymore in the control of the applications. In this thesis, we introduce a software paradigm based on object orientation in which real-time concurrent objects are enabled to specify their own scheduling strategy. We developed high-level formal models for specifying distributed software based on this paradigm in which the quality of service requirements are specified as deadlines on performing and finishing tasks. At this level we developed techniques to verify that these requirements are satisfied. This research has opened the way to a new approach to modeling and analysis of a range of applications such as continuous planning in the context of logistics software in a dynamic environment as well as developing software for multi-core systems. Industrial companies (DEAL services) and research centers (the Uppsala Programming for Multicore Architectures Resrearch Center UPMARC) have already shown interest in the results of this thesis.LEI Universiteit LeidenFoundations of Software Technolog