Effective representation of RT-LOTOS terms by finite time petri nets

The paper describes a transformational approach for the specification and formal verification of concurrent and real-time systems. At upper level, one system is specified using the timed process algebra RT-LOTOS. The output of the proposed transformation is a Time Petri net (TPN). The paper particularly shows how a TPN can be automatically constructed from an RT-LOTOS specification using a compositionally defined mapping. The proof of the translation consistency is sketched in the paper and developed in [1]. The RT-LOTOS to TPN translation patterns formalized in the paper are being implemented. in a prototype tool. This enables reusing TPNs verification techniques and tools for the profit of RT-LOTOS

Performance evaluation of an emergency call center: tropical polynomial systems applied to timed Petri nets

We analyze a timed Petri net model of an emergency call center which processes calls with different levels of priority. The counter variables of the Petri net represent the cumulated number of events as a function of time. We show that these variables are determined by a piecewise linear dynamical system. We also prove that computing the stationary regimes of the associated fluid dynamics reduces to solving a polynomial system over a tropical (min-plus) semifield of germs. This leads to explicit formul{\ae} expressing the throughput of the fluid system as a piecewise linear function of the resources, revealing the existence of different congestion phases. Numerical experiments show that the analysis of the fluid dynamics yields a good approximation of the real throughput.Comment: 21 pages, 4 figures. A shorter version can be found in the proceedings of the conference FORMATS 201

Indefinite waitings in MIRELA systems

MIRELA is a high-level language and a rapid prototyping framework dedicated to systems where virtual and digital objects coexist in the same environment and interact in real time. Its semantics is given in the form of networks of timed automata, which can be checked using symbolic methods. This paper shows how to detect various kinds of indefinite waitings in the components of such systems. The method is experimented using the PRISM model checker.Comment: In Proceedings ESSS 2015, arXiv:1506.0325

P♤ : A process algebra for modeling prioritized stochastic timed systems (extended abstract)

We present P♤, a Stochastic Process Algebra (SPA) that allows for the modeling of timed systems with priorities and urgency. We de ne the semantics of P♤ in terms of Prioritized Stochastic Automata (PSA), an extension of automata with clock events, priorities and probabilistic symbolic transitions. PSAs are symbolic objects that have a concrete semantics on Probabilistic Timed Transition Systems (PTTS). Therefore, P♤ has semantics in two steps in terms of PTTS. We also de ne several operators directly on PTTS. They include parallel composition and a prioritizing operator. We show that this operators applied to PTTS commute (modulo probabilistic bisimulation) with their relatives in P♤ .Eje: Teoría (TEOR)Red de Universidades con Carreras en Informática (RedUNCI

Modeling Bitcoin Contracts by Timed Automata

Bitcoin is a peer-to-peer cryptographic currency system. Since its introduction in 2008, Bitcoin has gained noticeable popularity, mostly due to its following properties: (1) the transaction fees are very low, and (2) it is not controlled by any central authority, which in particular means that nobody can "print" the money to generate inflation. Moreover, the transaction syntax allows to create the so-called contracts, where a number of mutually-distrusting parties engage in a protocol to jointly perform some financial task, and the fairness of this process is guaranteed by the properties of Bitcoin. Although the Bitcoin contracts have several potential applications in the digital economy, so far they have not been widely used in real life. This is partly due to the fact that they are cumbersome to create and analyze, and hence risky to use. In this paper we propose to remedy this problem by using the methods originally developed for the computer-aided analysis for hardware and software systems, in particular those based on the timed automata. More concretely, we propose a framework for modeling the Bitcoin contracts using the timed automata in the UPPAAL model checker. Our method is general and can be used to model several contracts. As a proof-of-concept we use this framework to model some of the Bitcoin contracts from our recent previous work. We then automatically verify their security in UPPAAL, finding (and correcting) some subtle errors that were difficult to spot by the manual analysis. We hope that our work can draw the attention of the researchers working on formal modeling to the problem of the Bitcoin contract verification, and spark off more research on this topic

Testing timed systems modeled by stream X-machines

Stream X-machines have been used to specify real systems where complex data structures. They are a variety of extended finite state machine where a shared memory is used to represent communications between the components of systems. In this paper we introduce an extension of the Stream X-machines formalism in order to specify systems that present temporal requirements. We add time in two different ways. First, we consider that (output) actions take time to be performed. Second, our formalism allows to specify timeouts. Timeouts represent the time a system can wait for the environment to react without changing its internal state. Since timeous affect the set of available actions of the system, a relation focusing on the functional behavior of systems, that is, the actions that they can perform, must explicitly take into account the possible timeouts. In this paper we also propose a formal testing methodology allowing to systematically test a system with respect to a specification. Finally, we introduce a test derivation algorithm. Given a specification, the derived test suite is sound and complete, that is, a system under test successfully passes the test suite if and only if this system conforms to the specification

Integrating verifiable Assume/Guarantee contracts in UML/SysML

International audienceThe compositional approach based on components and driven by requirements is a common method used in the development of critical real-time embedded systems. Since the satisfaction of a requirement is subject to the composition of several components, defining abstract and partial behaviors for components with respect to the point of view of the requirement allows for a manageable design of systems. In this paper we consider such specifications in the form of contracts. A contract for a component is a pair (assumption, guarantee) where the assumption is an abstraction of the component's environment behavior and the guarantee is an abstraction of the component's behavior given that the environment behaves like the assumption. In previous work we have defined a formal contract-based theory for Timed Input/Output Automata with the aim of using it to express the semantics of UML/SysML models. In this paper we propose an extension of the UML/SysML language with a syntax and semantics for contracts and for the relations they must satisfy. Besides the important role that contracts have in design, they can also be used for the verification of requirement satisfaction and for their traceability