Read Operators and their Expressiveness in Process Algebras

We study two different ways to enhance PAFAS, a process algebra for modelling asynchronous timed concurrent systems, with non-blocking reading actions. We first add reading in the form of a read-action prefix operator. This operator is very flexible, but its somewhat complex semantics requires two types of transition relations. We also present a read-set prefix operator with a simpler semantics, but with syntactic restrictions. We discuss the expressiveness of read prefixes; in particular, we compare them to read-arcs in Petri nets and justify the simple semantics of the second variant by showing that its processes can be translated into processes of the first with timed-bisimilar behaviour. It is still an open problem whether the first algebra is more expressive than the second; we give a number of laws that are interesting in their own right, and can help to find a backward translation.Comment: In Proceedings EXPRESS 2011, arXiv:1108.407

Code Mobility for Pervasive Computing

In this paper we isolate and implement the minimal functionalities for an open platform supporting mobile code. The use of the platform is discussed in the context of pervasive and ubiquitous computing. We also present a calculus for modelling mobile applications

Fairness of components in system computations

In this paper we provide a simple characterization of (weak) fairness of components as defined by Costa and Stirling. The study is carried out at system specification level by resorting to a common process description language. This paper follows and exploits similar techniques as those developed in an earlier paper -- where fairness of actions was taken into account and was contrasted to the PAFAS timed operational semantics -- but the characterization of fair executions is based on a new semantics for PAFAS; it makes use of only two copies of each basic action instead of infinitely many and allows for a simple and finite representation of fair executions by using regular expressions. The new semantics can also be understood as describing timed behaviour of systems with upper time bounds. The paper discusses in detail how this new semantics differs from the old one, and why theses changes are necessary to properly capture fairness of components

Shape Calculus: A spatial calculus for 3D colliding shapes

Available at http://s1report.cs.unicam.it/6

Automated Analysis of MUTEX Algorithms with FASE

In this paper we study the liveness of several MUTEX solutions by representing them as processes in PAFAS s, a CCS-like process algebra with a specific operator for modelling non-blocking reading behaviours. Verification is carried out using the tool FASE, exploiting a correspondence between violations of the liveness property and a special kind of cycles (called catastrophic cycles) in some transition system. We also compare our approach with others in the literature. The aim of this paper is twofold: on the one hand, we want to demonstrate the applicability of FASE to some concrete, meaningful examples; on the other hand, we want to study the impact of introducing non-blocking behaviours in modelling concurrent systems.Comment: In Proceedings GandALF 2011, arXiv:1106.081

Fairness of actions in system computations

This paper contrasts two important features of parallel system computations: fairness and timing. The study is carried out at specification system level by resorting to a well-known process description language. The language is extended with labels which allow to filter out those process executions that are not (weakly) fair, and with upper time bounds for the process activities. We show that fairness and timing are closely related. Two main results are stated. First, we show that each everlasting (or non-Zeno) timed process execution is fair. Second, we provide a characterization for fair executions of untimed processes in terms of timed process executions. This results in a finite representation of fair executions using regular expressions

Time and fairness in a process algebra with non-blocking reading

We introduce the first process algebra with non-blocking reading actions for modelling concurrent asynchronous systems. We study the impact this new kind of actions has on fairness, liveness and the timing of systems, using as application Dekker’s mutual exclusion algorithm we already considered in [4]. Regarding some actions as reading, this algorithm satisfies MUTEX liveness already under the assumption of fairness of actions. We demonstrate an interesting correspondence between liveness and the catastrophic cycles that we introduced in [6] when studying the performance of pipelining. Finally, our previous result on the correspondence between timing and fairness [4] scales up to the extended language

Relating fairness and timing in process algebras

This paper contrasts two important features of parallel system computations: fairness and timing. The study is carried out at specification system level by resorting to a well-known process description language. The language is extended with labels which allow to filter out those process executions that are not (weakly) fair (as in [5,6]), and with upper time bounds for the process activities (as in [2]). We show that fairness and timing are closely related. Two main results are stated. First, we show that each everlasting (or non-Zeno) timed process execution is fair. Second, we provide a characterization for fair executions of untimed processes in terms of timed process executions. This results in a finite representation of fair executions using regular expression