Structural Translation of Time Petri Nets into Timed Automata

International audienceIn this paper, we consider Time Petri Nets (TPN) where time is associated with transitions. We give a formal semantics for TPNs in terms of Timed Transition Systems. Then, we propose a translation from TPNs to Timed Automata (TA) that preserves the behavioural semantics (timed bisimilarity) of the TPNs. For the theory of TPNs this result is two-fold: i) reachability problems and more generally TCTL model-checking are decidable for bounded TPNs; ii) allowing strict time constraints on transitions for TPNs preserves the results described in i). The practical applications of the translation are: i) one can specify a system using both TPNs and Timed Automata and a precise semantics is given to the composition; ii) one can use existing tools for analysing timed automata (like KRONOS or UPPAAL or CMC) to analyse TPNs

Zone-based formal specification and timing analysis of real-time self-adaptive systems

Self-adaptive software systems are able to autonomously adapt their behavior at run-time to react to internal dynamics and to uncertain and changing environment conditions. Formal specification and verification of self-adaptive systems are tasks generally very difficult to carry out, especially when involving time constraints. In this case, in fact, the system correctness depends also on the time associated with events. This article introduces the Zone-based Time Basic Petri nets specification formalism. The formalism adopts timed adaptation models to specify self-adaptive behavior with temporal constraints, and relies on a zone-based modeling approach to support separation of concerns. Zones identified during the modeling phase can be then used as modules either in isolation, to verify intra-zone properties, or all together, to verify inter-zone properties over the entire system. In addition, the framework allows the verification of (timed) robustness properties to guarantee self-healing capabilities when higher levels of reliability and availability are required to the system, especially when dealing with time-critical systems. This article presents also the ZAFETY tool, a Java software implementation of the proposed framework, and the validation and experimental results obtained in modeling and verifying two time-critical self-adaptive systems: the Gas Burner system and the Unmanned Aerial Vehicle system

Temporal Logic Motion Planning

In this paper, a critical review on temporal logic motion planning is presented. The review paper aims to address the following problems: (a) In a realistic situation, the motion planning problem is carried out in real-time, in a dynamic, uncertain and ever-changing environment, and (b) The accomplishment of high-level specification tasks which are more than just the traditional planning problem (i.e., start at initial state A and go to the goal state B) are considered. The use of theory of computation and formal methods, tools and techniques present a promising direction of research in solving motion planning problems that are influenced by high-level specification of complex tasks. The review, therefore, focuses only on those papers that use the aforementioned tools and techniques to solve a motion planning problem. A proposed robust platform that deals with the complexity of more expressive temporal logics is also presented.Defence Science Journal, 2010, 60(1), pp.23-38, DOI:http://dx.doi.org/10.14429/dsj.60.9

Integrated Modeling and Verification of Real-Time Systems through Multiple Paradigms

Complex systems typically have many different parts and facets, with different characteristics. In a multi-paradigm approach to modeling, formalisms with different natures are used in combination to describe complementary parts and aspects of the system. This can have a beneficial impact on the modeling activity, as different paradigms an be better suited to describe different aspects of the system. While each paradigm provides a different view on the many facets of the system, it is of paramount importance that a coherent comprehensive model emerges from the combination of the various partial descriptions. In this paper we present a technique to model different aspects of the same system with different formalisms, while keeping the various models tightly integrated with one another. In addition, our approach leverages the flexibility provided by a bounded satisfiability checker to encode the verification problem of the integrated model in the propositional satisfiability (SAT) problem; this allows users to carry out formal verification activities both on the whole model and on parts thereof. The effectiveness of the approach is illustrated through the example of a monitoring system.Comment: 27 page

On the decidability and complexity of Metric Temporal Logic over finite words

Metric Temporal Logic (MTL) is a prominent specification formalism for real-time systems. In this paper, we show that the satisfiability problem for MTL over finite timed words is decidable, with non-primitive recursive complexity. We also consider the model-checking problem for MTL: whether all words accepted by a given Alur-Dill timed automaton satisfy a given MTL formula. We show that this problem is decidable over finite words. Over infinite words, we show that model checking the safety fragment of MTL--which includes invariance and time-bounded response properties--is also decidable. These results are quite surprising in that they contradict various claims to the contrary that have appeared in the literature

Formal modelling and analysis of broadcasting embedded control systems

PhD ThesisEmbedded systems are real-time, communicating systems, and the effective modelling and analysis of these aspects of their behaviour is regarded as essential for acquiring confidence in their correct operation. In practice, it is important to minimise the burden of model construction and to automate the analysis, if possible. Among the most promising techniques for real-time systems are reachability analysis and model-checking of networks of timed automata. We identify two obstacles to the application of these techniques to a large class of distributed embedded systems: firstly, the language of timed automata is too low-level for straightforward model construction, and secondly, the synchronous, handshake communication mechanism of the timed automata model does not fit well with the asynchronous, broadcast mechanism employed in many distributed embedded systems. As a result, the task of model construction can be unduly onerous. This dissertation proposes an expressive language for the construction of models of real-time, broadcasting control systems, and demonstrates how effi- cient analysis techniques can be applied to them. The dissertation is concerned in particular with the Controller Area Network (CAN) protocol which is emerging as a de facto standard in the automotive industry. An abstract formal model of CAN is developed. This model is adopted as the communication primitive in a new language, bCANDLE, which includes value passing, broadcast communication, message priorities and explicit time. A high-level language, CANDLE, is introduced and its semantics defined by translation to bCANDLE. We show how realistic CAN systems can be described in CANDLE and how a timed transition model of a system can be extracted for analysis. Finally, it is shown how efficient methods of analysis, such as 'on-the- fly' and symbolic techniques, can be applied to these models. The dissertation contributes to the practical application of formal methods within the domain of broadcasting, embedded control systemsSchool of Computing and Mathematics at the University of Northumbri

Master of Science

thesisThis document describes an improved method of formal verification of complex analog/mixed-signal (AMS) circuits. Currently, in our LEMA tool, verification properties are encoded using labeled Petri net (LPN). These LPNs are generated manually, a tedious process that requires the user to have considerable familiarity with the tool. To eliminate this time-consuming process, our LEMA tool is extended to include a translator that converts properties written in a property specification language to LPNs. New methods are also implemented to separate the transient period from the stable output period, thus improving the generated model. Also, the current methodology generates the circuit models for the input values used during the simulation of the circuit. So, models generated for other control input values are not accurate. In this case, accuracy of the generated models is improved by using a linear abstraction method like interpolation

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