Abstract not found

A novel form of labelled transition system is proposed, where the labels are the arrows of a category, and adjacent labels in computations are required to be composable. Such transition systems provide the foundations for modular SOS descriptions of programming languages. Three

Modularity is an important pragmatic aspect of semantic descriptions. In denotational semantics, the issue of modularity has received much attention, and appropriate abstractions have been introduced, so that definitions of semantic functions may be independent of the details of how computations are modelled. In structural operational semantics (SOS), however, this issue has largely been neglected, and SOS descriptions of programming languages typically exhibit rather poor modularity -- for instance, extending the described language may entail a complete reformulation of the description of the original constructs. A propos

. Mobile agents, i.e. pieces of programs that can be sent around networks of computers, are starting to appear on the Internet. Such programs may be seen as an enrichment of traditional distributed computing. Since mobile agents may carry communication links with them as they move across the network, they create very dynamic interconnection structures that can be extremely complex to analyse. In this paper we analyse a fragment of a system based on the mobile agent principle written in the Facile programming language. We propose a Structural Operational Semantics (SOS) for Facile, giving a proved transition system that records encodings of the derivation trees of transitions in their labels. This information allows us to easily recover non-interleaving semantics for Facile by looking only at the labels of transitions. We use the new Facile semantics to debug an agent based system. This example is a scaled down version of a system demonstrated at the European IT Conference Exhibition in...

We investigate confluence properties for concurrent systems of message-passing processes, because such properties have proved to be useful for a variety of applications, ranging from reasoning about concurrent objects to mobile and high-speed telecommunication protocols. Roughly, confluence means that for every two computations starting from a common system state, it is possible to continue the computations, so to reach a common state again. In order to prove confluence for a given system, we are required to demonstrate that for all states reachable by computation from the starting state, the `flowing together' of possible computations is possible. In this paper, we aim at proving con#uence properties for concurrent systems without having to generate all reachable states. Instead, we use a type system that supports a static analysis of possible sources of non-confluence. In message-passing systems, confluence is invalidated whenever two processes compete for communication with another proce...

Various logic-based frameworks have been proposed for specifying the operational semantics of programming languages and concurrent systems, including inference systems in the styles advocated by Plotkin and by Kahn, Horn logic, equational specifications, reduction systems for evaluation contexts, rewriting logic, and tile logic. We consider

Both for interleaving and for non-interleaving semantics, several variants of a pi-calculus bisimilarity can be given which differ on the requirements imposed on name instantiations. Examples are the late, early, open and ground variants. The ground variant is the simplest because it places no requirements on name instantiations. With the exception of open bisimilarities, none of the bisimilarity considered in the literature is a congruence relation on the full pi-calculus language. We show that in the case of (certain forms of) causal bisimulation the late, early, open and ground variants coincide and are congruence relations in the sublanguage of the pi-calculus without matching. We also show that to obtain the same results in the case of the interleaving bisimilarity, in addition to forbidding matching it is necessary to constrain the output prefix.

. Mobile agents, i.e. pieces of programs that can be sent around networks of computers, are starting to appear on the Internet. Such programs may be seen as an enrichment of traditional distributed computing. Since mobile agents may carry communication links with them as they move across the network, they create very dynamic interconnection structures that can be extremely complex to analyse. In this paper we apply a non-interleaving semantics to analyse a system based on the mobile agent principle written in the Facile programming language. This example is a scaled down version of a system demonstrated at the European IT Conference Exhibition in Brussels, 1995. This paper further develops a non-interleaving semantics for Facile, first presented in [4]. We develop a Structural Operational Semantics (SOS) for Facile, giving a proved transition system that records encodings of the derivation trees of transitions in their labels. This information allows us to easily recover non-interleavi...

In this study we extend stochastic ß-calculus allowing general probabilistic distributions to occur in its prefixes. We show that no additional information is needed in the labels of transitions or in the states of systems to derive an enabling relation between transitions. Enabling is then used to compute the residual life times of parallel activities that are not immediately selected when enabled. The policy according to which residual life times are computed is the enabling memory introduced for stochastic Petri nets and also implemented in TIPP through the mechanism of start references. 1 Introduction Many researchers advocate the need of integrating behavioural and performance analysis since the early stages of design of complex systems. This problem is even presented as a challenge for the future of computer science in [11]. The widespread dissemination of distributed systems and the paradigm of mobile computing makes the above integration essential. In fact, a design error whic...

In this paper we present a partial ordering semantics for the ß-calculus. The model we adopt is transition system based. In spite of their interleaving nature, we show that it is possible to completely abstract from the generation ordering of transitions. The definition of this semantics drive us in defining a standard SOS semantics that directly yields the partial ordering semantics of ß-calculus. 1 Introduction In recent times, distributed systems are receiving more and more attention due to their widespread dissemination. The design, implementation and maintenance of these systems is a difficult task because of the large amount of details that must be taken into account. This imposes the use of formal techniques to ensure reliability. Since the life-cycle of distributed and concurrent systems involves people with many different backgrounds, the formalisms used to drive the realization must be simple and must allow different views of the same system. In fact, the designer may be in...