Francesco Spegni

Parameterized Model Checking of Rendezvous Systems

A standard technique for solving the parameterized model checking problem is to reduce it to the classic model checking problem of finitely many finite-state systems. This work considers some of the theoretical power and limitations of this technique. We focus on concurrent systems in which processes communicate via pairwise rendezvous, as well as the special cases of disjunctive guards and token passing; specifications are expressed in indexed temporal logic without the next operator; and the underlying network topologies are generated by suitable Monadic Second Order Logic formulas and graph operations. First, we settle the exact computational complexity of the parameterized model checking problem for some of our concurrent systems, and establish new decidability results for others. Second, we consider the cases that model checking the parameterized system can be reduced to model checking some fixed number of processes, the number is known as a cutoff. We provide many cases for when such cutoffs can be computed, establish lower bounds on the size of such cutoffs, and identify cases where no cutoff exists. Third, we consider cases for which the parameterized system is equivalent to a single finite-state system (more precisely a Buchi word automaton), and establish tight bounds on the sizes of such automata.

Liveness of Parameterized Timed Networks

We consider the model checking problem of infinite state systems given in the form of parameterized discrete timed networks with multiple clocks. We show that this problem is decidable with respect to specifications given by B- or S-automata. Such specifications are very expressive they strictly subsume

Dynamic Networks of Timed Automata for collaborative systems: A network monitoring case study

\omega

Parametric and probabilistic model checking of confidentiality in data dispersal algorithms

-regular specifications, and easily express complex liveness and safety properties. Our results are obtained by modeling the passage of time using symmetric broadcast, and by solving the model checking problem of parameterized systems of untimed processes communicating using k-wise rendezvous and symmetric broadcast. Our decidability proof makes use of automata theory, rational linear programming, and geometric reasoning for solving certain reachability questions in vector addition systems; we believe these proof techniques will be useful in solving related problems.

A Probabilistic Small Model Theorem to Assess Confidentiality of Dispersed Cloud Storage

In this work we extend the Emerson and Kahlons cutoff theorems for process skeletons with conjunctive guards to Parameterized Networks of Timed Automata, i.e. systems obtained by an \emph{apriori} unknown number of Timed Automata instantiated from a finite set

A modular environment for software development and re-engineering

U_1, \dots, U_n

Modeling time in Java programs for automatic error detection

of Timed Automata templates. In this way we aim at giving a tool to universally verify software systems where an unknown number of software components (i.e. processes) interact with continuous time temporal constraints. It is often the case, indeed, that distributed algorithms show an heterogeneous nature, combining dynamic aspects with real-time aspects. In the paper we will also show how to model check a protocol that uses special variables storing identifiers of the participating processes (i.e. PIDs) in Timed Automata with conjunctive guards. This is non-trivial, since solutions to the parameterized verification problem often relies on the processes to be symmetric, i.e. indistinguishable. On the other side, many popular distributed algorithms make use of PIDs and thus cannot directly apply those solutions.

Parameterized model checking of rendezvous systems

We introduce Dynamic Networks of Timed Automata, an extension of (Networks of) Timed Automata useful for specifying concurrently executing timed-processes. The main difference with Timed Automata is that we allow the instantiation at run-time of multiple copies of automata. In this paper we also show an industrial case study where a system for monitoring a network of wireless devices is built applying Dynamic Networks of Timed Automata. The network is characterized by a high degree of dynamism, since its infrastructure is fixed but a big amount of its hosts continuously connect and disconnect. We see how extending XAL, an executable language for Timed Automata, we can first model our system, made of cooperating timed processes, and finally transform such model into an executable application. We also show how to model-check relevant properties of our application, expressing them through a temporal logic called TCTL and using existing formal methods and tools.