Simone Tini

Equivalences of Statecharts

We present a new semantics of Statecharts that excludes failures and a compositional formulation of this semantics based on Labelled Transition Systems (LTS). We consider a hierarchy of LTS equivalences and we study their congruence properties w.r. to statechart operators.

Compositional semantics and behavioral equivalences for P Systems

The aim of the paper is to give a compositional semantics in the style of the Structural Operational Semantics (SOS) and to study behavioral equivalence notions for P Systems. Firstly, we consider P Systems with maximal parallelism and without priorities. We define a process algebra, called P Algebra, whose terms model membranes, we equip the algebra with a Labeled Transition System (LTS) obtained through SOS transition rules, and we study how some equivalence notions defined over the LTS model apply in our case. Then, we consider P Systems with priorities and extend the introduced framework to deal with them. We prove that our compositional semantics reflects correctly maximal parallelism and priorities.

Probabilistic congruence for semistochastic generative processes

We propose an SOS transition rule format for the generative model of probabilistic processes. Transition rules are partitioned in several strata, giving rise to an ordering relation analogous to those introduced by Ulidowski and Phillips for classic process algebras. Our rule format guarantees that probabilistic bisimulation is a congruence w.r.t. process algebra operations. Moreover, our rule format guarantees that process algebra operations preserve semistochasticity of processes, i.e. the property that the sum of the probability of the moves of any process is either 0 or 1. Finally, we show that most of operations of the probabilistic process algebras studied in the literature are captured by our format, which, therefore, has practical applications.

A comparison of Statecharts step semantics

The paper studies some variants of Statecharts step semantics in the framework of structural operational semantics. The chosen framework allows to study precongruence and congruence properties of behavioral preorders and equivalences and to compare, with respect to these properties, the different step semantics considered.

On the expressiveness of Timed Concurrent Constraint Programming

Abstract We prove that both the synchronous data flow language Lustre restricted to finite value types and the synchronous state oriented language Argos are embedded in the synchronous paradigm Timed Concurrent Constraint (tcc). In fact, for each of the two languages we provide a tcc language encoding it compositionally w.r. to the structure of programs. Moreover, we prove that the “strong abortion” mechanism of the synchronous imperative language Esterel can be encoded in tcc.

Probabilistic bisimulation as a congruence

We propose both an SOS transition rule format for the generative model of probabilistic processes, and an SOS transition rule format for the reactive model of the probabilistic processes. Our rule formats guarantee that probabilistic bisimulation is a congruence with respect to process algebra operations. Moreover, our rule format for generative process algebras guarantees that the probability of the moves of a given process, if there are any, sum up to 1, and the rule format for reactive process algebras guarantees that the probability of the moves of a given process labeled with the same action, if there are any, sum up to 1. We show that most operations of the probabilistic process algebras studied in the literature are captured by our formats, which, therefore, have practical applications.

Rule formats for compositional non-interference properties

We introduce the transition rule formats rooted SBSNNI and CP_BNDC. We prove that the non-interference property rooted SBSNNI introduced in the present paper, and the already known non-interference property CP_BNDC, are preserved by constructs of all process algebras with SOS transition rules respecting the restrictions of the formats rooted SBSNNI and CP_BNDC, respectively. To show that our formats have practical applications, we prove that a slight variant of Focardi and Gorrieris Security Process Algebra, the Kleene star recursion construct, the replication construct of polyadic π-calculus, and a process algebra extending BPAϵτ to deal with two level systems, respect both formats. By means of some counterexamples, we prove also that all restrictions of the formats are necessary.

Taylor approximation for hybrid systems

We propose a new approximation technique for Hybrid Automata. Given any Hybrid Automaton H, we call Approx(H,k) the Polynomial Hybrid Automaton obtained by approximating each formula φ in H with the formulae φk obtained by replacing the functions in φ with their Taylor polynomial of degree k. We prove that Approx(H,k) is an over–approximation of H. We study the conditions ensuring that, given any e > 0, some k0 exists such that, for all k>k0, the “distance” between any vector satisfying φk and at least one vector satisfying φ is less than e. We study also conditions ensuring that, given any e > 0, some k0 exists such that, for all k > k0, the “distance” between any configuration reached by Approx(H,k) in n steps and at least one configuration reached by H in n steps is less than e.

Compositionality of Approximate Bisimulation for Probabilistic Systems

Probabilistic transition system specifications using the rule format ntmuft-ntmuxt provide structural operational semantics for Segala-type systems and guarantee that probabilistic bisimilarity is a congruence. Probabilistic bisimilarity is for many applications too sensitive to the exact probabilities of transitions. Approximate bisimulation provides a robust semantics that is stable with respect to implementation and measurement errors of probabilistic behavior. We provide a general method to quantify how much a process combinator expands the approximate bisimulation distance. As a direct application we derive an appropriate rule format that guarantees compositionality with respect to approximate bisimilarity. Moreover, we describe how specification formats for non-standard compositionality requirements may be derived.

AN OVERVIEW ON OPERATIONAL SEMANTICS IN MEMBRANE COMPUTING

The aim of this paper is to give motivations for the development of operational semantics in membrane computing, and to survey existing proposals. In particular, the definitions are compared of three operational semantics available in the literature, namely a semantics proposed by Andrei, Ciobanu and Lucanu, another proposed by Busi, and another one proposed by the authors of the present paper. These definitions are different since they are given with different aims. However, we show that there is an operational correspondence among the three.