Timed Automata Research Articles

A logical characterization of timed regular languages

CLTLoc (Constraint LTL over clocks) is a quantifier-free extension of LTL allowing variables behaving like clocks over real numbers. CLTLoc is in PSPACE [1] and its satisfiability can polynomially be reduced to a Satisfiability Modulo Theories (SMT) problem, allowing a feasible implementation of a decision procedure. We used CLTLoc to capture the semantics of metric temporal logics over continuous time, such as Metric Interval Temporal Logic (MITL), resulting in the first successful implementation of a tool for checking MITL satisfiability [2,3]. In this paper, we assess the expressive power of CLTLoc, by comparing it with various temporal formalisms over dense time. We restrict the analysis to well initialized models of formulae where the value of all clocks in the origin is either 0 or equal to a positive real constant. Under this assumption, when interpreted over timed words, the class of timed languages defined by CLTLoc formulae coincides with the class defined by Timed Automata. We also define a timed monadic first order logic of order, extending the one introduced by Kamp, which is expressively equivalent to CLTLoc for the class of timed languages that are defined by well initialized models.

Model Checking of Non-Centralized Automaton Web Service with AMT Bounded Constraint

In view of the web service model checking application, the combination mode of traditional finite state machines cannot guarantee the correctness of Web composite service. A web service model diction algorithm of non-centralized automaton based on satisfiability modulo theories (SMT) is proposed. First, SMT is used for bounded model checking of time automaton, and the time automaton model is directly converted into logical formula that can be identified by SMT, to make solution; secondly, the proposed SMT time automaton theory is used to achieve the employee travel arrangements web services for modeling and verification; finally, through an example analysis, the effectiveness of the algorithm on the termination of the path deadlock and the optimization of network parameters.

To Simplification of Timed Automata During Synchronization of Components of Physical Systems

Possibilities of reduction of the number of time variables in a timed automaton used for synchronization of components in physical systems, for example, lasers are investigated. Reduction of the number of time variables allows problems of testing of the components for compliance with requirement specification to be simplified.

Comparison of Timed Automata with Discrete Event Simulation for Modeling Personalized Treatment Decisions: the Case of Metastatic Castration Resistant Prostate Cancer

Objectives The aim of this study is to compare the usefulness of two promising alternative modeling techniques, Timed Automata (TA) originating from informatics, and Discrete Event Simulation (DES) known in operations research, for modeling todays complex and personalized treatment decisions over time, involving multiple interactions and decision gates. Methods The usefulness of both modeling techniques was assessed in a case study on the treatment of metastatic Castration Resistant Prostate Cancer (mCRPC) in which Circulating Tumor Cells (CTC) may be used as a response marker for switching first to second line treatment. Techniques were compared on user-friendliness, input requirements, input possibilities, model checking facilities, and results. Input parameters were similar for both models, consisting of costs, QoL, treatment effectiveness, diagnostic performance, physicians’ behavior and survival. Primary outcome measures were health outcomes, expressed in QALYs, and costs. Results Modelling was considered easier using TA, as this approach allows independent modeling of the actors and elements comprising the treatment process, such as patients, physicians, tests and treatments, and their mutual interaction and communication. Furthermore, the statistical model checking feature in the TA software was found to be a powerful tool for validation. Input requirements and possibilities were similar for both modelling approaches in this case study. Both modelling approaches yield comparable results. Using TA, CTC reduced first and second line treatment by, on average, 108.9 and 107.6 days, respectively. Using DES, treatment was reduced by 83.6 and 85.0 days. CTC therefore reduced healthcare costs by €28,998 and €21,992 according to TA and DES, respectively. Conclusions Both Timed Automata and Discrete Event Simulation seem to be suitable for modeling complex and personalized treatment processes like that of mCRPC. Timed Automata is a new and interesting alternative modeling technique, as it allows explicit separation of model components and supports statistical model checking to validate models.

Approach to analyzing AADL end-to-end flow latency based on timed automata

End-to-end flow latency analysis of complex embedded system is an effective way to assess system's real-time performance. Architecture analysis and design language( AADL) is the standard language to specify the architecture of complex embedded system,end-to-end flow of which describes the components' interaction. At present,most manual latency analysis approaches could consider flow's precise semantics. However,the efficiency of this time consuming analysis is low; although automatic methods have better efficiency,the accuracy is not satisfying because of the low coverage of delay-contribution attributes. What's more,both kinds of methods only focus on the typical interactive situations such as the worst-latency analysis. The impact of design elements resulting in uncertainty cannot be analyzed. Thus,one approach to analyzing AADL end-toend flow latency based on timed automata model was proposed. First,latency-contributed attributes meta-model of flow was constructed to improve the coverage of latency-contributed attributes. Then the transformation from AADL end-to-end flow to timed automata model was studied. Latency analyzing was performed through simulating the timed automata model. Finally,the experiments based on one case study demonstrate that our way can precisely model the transportation semantics and the latency attributes semantics of a flow,illustrating our way's sufficient expressive competence. Additionally,the experiments also show flexible analysis ability of our approach by dealing with the various interactive scenarios and even the random time factors in the transportation of information. Meanwhile,the state transition and the changing on the time factors provide a basis and suggestions for the further improvement of the original AADL model.

Accelerating worst case execution time analysis of timed automata models with cyclic behaviour

Abstract The paper presents a new efficient algorithm for computing worst case execution time (WCET) of systems modelled as timed automata (TA). The algorithm uses a set of abstraction techniques that improve significantly the efficiency of WCET analysis of TA models with cyclic behaviour. We show that the proposed abstractions are exact with respect to the WCET problem in the sense that the WCET computed in the abstract model is equal to the one computed in the concrete model. We also compare our algorithm with the one implemented in the model checker UPPAAL which shows that when infinite cycles exist (i.e. cycles that can be run infinitely often), UPPAAL’s algorithm may not terminate, and when largely repetitive finite cycles exist (i.e. cycles that can be run a large number of times but finite), UPPAAL’s algorithm suffers from the state space explosion, thus leading to a low efficiency or resource exhaustion.

Advances in the study of elementary cellular automata regular language complexity

Cellular automata (CA) are discrete dynamical systems that, out of the fully local action of its state transition rule, are capable of generating a multitude of global patterns, from the trivial to the arbitrarily complex ones. The set of global configurations that can be obtained by iterating a one‐dimensional cellular automaton for a finite number of times can always be described by a regular language. The size of the minimum finite automaton corresponding to such a language at a given time step provides a complexity measure of the underlying rule. Here, we study the time evolution of elementary CA, in terms of such a regular language complexity. We review and expand the original results on the topic, describe an alternative method for generating the subsequent finite automata in time, and provide a method to analyze and detect patterns in the complexity growth of the rules. © 2015 Wiley Periodicals, Inc. Complexity 21: 267–279, 2016

State-based real-time analysis of SDF applications on MPSoCs with shared communication resources

The timing predictability of Multi-Processor System on Chip (MPSoC) platforms with hard real-time applications is much more challenging than that of traditional platforms due to their large number of shared processing, communication and memory resources. Yet, this is an indispensable challenge for guaranteeing their safe usage in safety critical domains (avionics, automotive).In this article, a real-time analysis based on model-checking is proposed. The model-checking based method allows guaranteeing timing bounds of multiple Synchronous Data Flow Application (SDFA) implementations. This approach utilizes timed automata (TA) as a common semantic model to represent WCET of software components (SDF actors) and shared communication resource access protocols for buses, DMA, private local and shared memories of the MPSoC. The resulting network of TA is analyzed using the UPPAAL model-checker for providing safe timing bounds of the implementation. Furthermore, we will show the extension of our previous system model enabling single-beat inter-processor communication style beside the burst-transfer style and provide the implementation of the complete set of TA templates capturing the considered system model.We demonstrate our approach using a multi-phase electric motor control algorithm (modeled as SDFA) mapped to Infineon's TriCore-based Aurix multicore hardware platform with both the burst and single-beat inter-processor communication styles. Our approach shows a significant precision improvement (up to a percentage improvement of 300%) compared with the worst-case bound calculation based on a pessimistic analytical upper-bound delays for every shared resource access. In addition, scalability is examined to demonstrate analysis feasibility for small parallel systems, up to 40 actors mapped to 4-tiles and up to 96 actors on a 2-tiles platforms.

On the Designing of Model Checkers for Real-Time Distributed Systems

To verify real-time properties of UML statecharts one may apply a UPPAAL, toolbox for model checking of real-time systems. One of the most suitable ways to specify an operational semantics of UML statecharts is to invoke the formal model of Hierarchical Timed Automata. Since the model language of UPPAAL is based on Networks of Timed Automata one has to provide a conversion of Hierarchical Timed Automata to Networks of Timed Automata. In this paper we describe this conversion algorithm and prove that it is correct w.r.t. UPPAAL query language which is based on the subset of Timed CTL.

Minimizing Deterministic Lattice Automata

Traditional automata accept or reject their input and are therefore Boolean. In contrast, weighted automata map each word to a value from a semiring over a large domain. The special case of lattice automata , in which the semiring is a finite lattice, has interesting theoretical properties as well as applications in formal methods. A minimal deterministic automaton captures the combinatorial nature and complexity of a formal language. Deterministic automata are used in runtime monitoring, pattern recognition, and modeling systems. Thus, the minimization problem for deterministic automata is of great interest, both theoretically and in practice. For deterministic traditional automata on finite words, a minimization algorithm, based on the Myhill-Nerode right congruence on the set of words, generates in polynomial time a canonical minimal deterministic automaton. A polynomial algorithm is known also for deterministic weighted automata over the tropical semiring. For general deterministic weighted automata, the problem of minimization is open. In this article, we study minimization of deterministic lattice automata. We show that it is impossible to define a right congruence in the context of lattices, and that no canonical minimal automaton exists. Consequently, the minimization problem is much more complicated, and we prove that it is NP-complete. As good news, we show that while right congruence fails already for finite lattices that are fully ordered, for this setting we are able to combine a finite number of right congruences and generate a minimal deterministic automaton in polynomial time.

Solving the time varying postman problems with timed automata

In this work, we present timed automata as a natural tool for posing and solving time varying postman problems. We show that these problems can be reduced to the problem of finding the shortest runs in our Timed Automata System (TAS) model. The problem can then be solved by incorporating the reachability analysis (RA) algorithm into a binary search framework. However, the scale of the TAS model is too large to adapt the RA algorithm embedded in the UppAal. Thus, we propose a composition strategy to transform the current TAS model into a Generalized Timed Automaton (GTA) model, such that the number of timed automata in our model decreases from to . Computational results show that the GTA model can solve small-sized instances optimally and that it can obtain a better optimality gap than those obtained by the cutting plane algorithm.

English

This paper models and supervises kernel railroad crossing (KRC) systems using timed Petri nets and focuses on the control synthesis method, which consists in computing new firing conditions for the timed automaton (TA) transitions so that the forbidden locations are no longer reachable. The system to be modeled and supervised using timed Petri nets is converted to a TA and is analyzed using automata so that the functioning of the system respects given specifications. The main reason of using automata is that although the timed Petri nets supervisor controls the system, it fails to define the time units needed for the undefined time of a transition. Simulation results show the soundness of KRC modeling and supervision in the sense of ensuring the safety and maximizing utility (the gate should be opened as long as possible).

A maximal entropy stochastic process for a timed automaton

Several ways of assigning probabilities to runs of timed automata (TA) have been proposed recently. When only the TA is given, a relevant question is to design a probability distribution which represents in the best possible way the runs of the TA. We give an answer to this question using a maximal entropy approach. We introduce our variant of a stochastic model, the stochastic process over runs, which permits to simulate random runs of any given length with a linear number of atomic operations. We adapt the notion of Shannon (continuous) entropy to such processes. Our main contribution is an explicit formula defining a process Y⁎ which maximizes the entropy. This ensures that, among the stochastic process over runs of a given TA, Y⁎ is the one that permits to sample runs of the TA in the most uniform way possible. Hence, our method could be used in a statistical model checking framework, providing a non-trivial yet natural way to generate runs in a quasi-uniform manner (described in the article). The formula defining Y⁎ is an adaptation of the so-called Shannon–Parry measure to the timed automata setting. We also show that Y⁎ enjoys well known properties in ergodic and information theory, namely, Y⁎ is ergodic and satisfies an asymptotic equipartition property.

How to make a simple tool for verification of real-time systems

To verify real-time properties of UML statecharts one may apply a UPPAAL, toolbox for model checking of real-time systems. One of the most suitable ways to specify an operational semantics of UML statecharts is to invoke the formal model of Hierarchical Timed Automata. Since the model language of UPPAAL is based on Networks of Timed Automata one has to provide a conversion of Hierarchical Timed Automata to Networks of Timed Automata. In this paper we describe this conversion algorithm and prove that it is correct w.r.t. UPPAAL query language which is based on the subset of Timed CTL.

Playing Games with Timed Automata

Playing Games with Timed Automata

Business Process Verification: The Application of Model Checking and Timed Automata


 
 
 The most important result to standardize the notation for graphical representation of Business Processes (BPs) is the Business Process Model and Notation (BPMN). Despite the BPs modeled with BPMN being able to support business designers, BPMN models are not appropriate to support the analysis phase. BPMN models have no formal seman- tics to conduct qualitative analysis (validation and verification). In this work is presented how Model Checking (MC) verification technique for software and Timed Automata (TA) formal language are integrated within a formal verification approach to check BPs mod- eled with BPMN. Also, are introduced a set of guideline to transform BPMN models into TA. The use of our approach allow to business analysts and designers to perform evaluation (i.e., qualitative analysis) of BPs, based on the formal specification of BP–task model with TA. The application of the approach is aimed to evaluate the behavior of the BP–task model with respect to business performance indicators (for instance, service time, waiting time or queue size) derived from business needs, as is shown in an instance of an enterprise–project related to Customer Relationship Management.
 
 

Web Service Composition Automation based on Timed Automata

Web service composition is a new direction in the research of service computing. To promote the portfolio, the key problem is to achieve efficient and automatic composition process. We propose the web service composition model based on timed automata. In the computing framework, we design the formal model and its construction algorithm; provide a web service interface description language and composition automation engine. In order to validate its performance, using UPPAAL as the service composition simulator, realized the automation process from independent web services into composite ones. The experimental results verify the feasibility of automatic service composition and the effectiveness of the proposed configuration.

Modeling biological pathway dynamics with timed automata.

Living cells are constantly subjected to a plethora of environmental stimuli that require integration into an appropriate cellular response. This integration takes place through signal transduction events that form tightly interconnected networks. The understanding of these networks requires capturing their dynamics through computational support and models. ANIMO (analysis of Networks with Interactive Modeling) is a tool that enables the construction and exploration of executable models of biological networks, helping to derive hypotheses and to plan wet-lab experiments. The tool is based on the formalism of Timed Automata, which can be analyzed via the UPPAAL model checker. Thanks to Timed Automata, we can provide a formal semantics for the domain-specific language used to represent signaling networks. This enforces precision and uniformity in the definition of signaling pathways, contributing to the integration of isolated signaling events into complex network models. We propose an approach to discretization of reaction kinetics that allows us to efficiently use UPPAAL as the computational engine to explore the dynamic behavior of the network of interest. A user-friendly interface hides the use of Timed Automata from the user, while keeping the expressive power intact. Abstraction to single-parameter kinetics speeds up construction of models that remain faithful enough to provide meaningful insight. The resulting dynamic behavior of the network components is displayed graphically, allowing for an intuitive and interactive modeling experience.

Modeling and Simulation of NFC Logical Layer Peer-to-Peer Mode using CPN and TA

Network communication technologies have been growing explosively due to the increasing demand on faster and simpler communication; hence, providing new communication technologies is a challenging task. To make this task easy, many researchers have developed different network modeling and simulation tools with different characteristics. In this paper, simulation of Near Field Communication (NFC) logical layer control protocol is proposed to investigate efficiency of NFC device in peer-to-peer mode. For this purpose, Colored Petri Net (CPN) and Timed Automata (TA) have been used for analyses. According to the results, CPN was better than TA for simulating NFC logical layer control protocol because it could provide more details on complex communication network. DOI: http://dx.doi.org/10.11591/ijece.v4i2.5154

Control System Design for Height Measurement of BGA Balls Based on Timed Automata

This paper presents a model, based on timed automata (TA), of a real-time control system to measure the heights of solder balls of ball grid arrays (BGAs) on a printed circuit board and to determine whether the BGAs pass the height inspection routine. The TA model is actually a network of five TA, namely User, Controller, Motion, Camera, and Light, synchronized through user-defined channels. The dynamics of system components are simplified by a time delay which can be determined through experiments or roughly by experience. The simulation and verification in UPPAAL show that the model works fine without deadlock, and procedures after user operations demonstrate proper timely cooperation among the automata. The main design of hardware and software for the control system based on the model is also given in this paper, which has been successfully implemented in our laboratory.