Abstract. A formulation of semantic theories for processes which is based on reduction relation and equational reasoning is studied. The new construction can induce meaningful theories for processes, both in strong and weak settings. The resulting theories in many cases coincide with, and sometimes generalise, observation-based formulation of behavioural equivalence. The basic construction of reduction-based theories is studied, taking a simple name passing calculus called \nu-calculus as an example. Results on other calculi are also briefly discussed.

We present a model of distributed computation which is based on a fragment of the pi-calculus relying on asynchronous communication. We enrich the model with the following features: the explicit distribution of processes to locations, the failure of locations and their detection, and the mobility of processes. Our contributions are two folds. At the specification level, we give a synthetic and flexible formalization of the features mentioned above. At the verification level, we provide original methods to reason about the bisimilarity of processes in the presence of failures.

The asynchronous pi-calculus is considered the basis of experimental programming languages (or proposal of programming languages) like Pict, Join, and Blue calculus. However, at a closer inspection, these languages are based on an even simpler calculus, called Local (L), where: (a) only the output capability of names may be transmitted; (b) there is no matching or similar constructs for testing equality between names. We study the basic operational and algebraic theory of Lpi. We focus on bisimulation-based behavioural equivalences, precisely on barbed congruence. We prove two coinductive characterisations of barbed congruence in Lpi, and some basic algebraic laws. We then show applications of this theory, including: the derivability of delayed input; the correctness of an optimisation of the encoding of call-by-name lambda-calculus; the validity of some laws for Join.

. While types for name passing calculi have been studied extensively in the context of sorting of polyadic ß-calculus [5, 34, 9, 28, 32, 19, 33, 10, 17], the same type abstraction is not possible in the monadic setting, which was left as an open issue by Milner [21]. We solve this problem with an extension of sorting which captures dynamic aspects of process behaviour in a simple way. Equationally this results in the full abstraction of the standard encoding of polyadic ß-calculus into the monadic one: the sorted polyadic ß-terms are equated by a basic behavioural equality in the polyadic calculus if and only if their encodings are equated in a basic behavioural equality in the typed monadic calculus. This is the first result of this kind we know of in the context of the encoding of polyadic name passing, which is a typical example of translation of high-level communication structures into ß- calculus. The construction is general enough to be extendable to encodings of calculi with mo...

In this dissertation we investigate presheaf models for concurrent computation. Our aim is to provide a systematic treatment of bisimulation for a wide range of concurrent process calculi. Bisimilarity is defined abstractly in terms of open maps as in the work of Joyal, Nielsen and Winskel. Their work inspired this thesis by suggesting that presheaf categories could provide abstract models for concurrency with a built-in notion of bisimulation. We show how

The main Linda coordination primitives (asynchronous communication, read operation, nonblocking in/rd predicates) are studied in a process algebraic setting. A lattice of eight languages is proposed, where its bottom element L is a process algebra differing from CCS only for the asynchrony of the output operation, while all the other languages in the lattice are obtained as extension of this basic language by adding some of the Linda coordination primitives. The observational semantics for these languages are all obtained as the coarsest congruences contained in the barbed semantics, where only tuples are observable. The lattice of the eight languages collapses to a smaller four-points lattice of different bisimulation-based semantics. Notably, for L this semantics is the standard notion of strong bisimulation, where inputs and outputs/tuples are treated symmetrically. Keywords: Coordination languages, Semantics of Linda, Process algebra. 1 Introduction The aim of this paper is to pr...

The asynchronous pi-calculus is a variant of the pi-calculus where message emission is non-blocking. Honda and Tokoro have studied a semantics for this calculus based on bisimulation. Their bisimulation relies on a modified transition system where, at any moment, a process can perform any input action. In this paper we propose a new notion of bisimulation for the asynchronous pi-calculus, dened on top of the standard labelled transition system. We give several characterizations of this equivalence including one in terms of Honda and Tokoro's bisimulation, and one in terms of barbed equivalence. We show that this bisimulation is preserved by name substitutions, hence by input prefix. Finally, we give a complete axiomatization of the (strong) bisimulation for finite terms.

In this work we present Bio-PEPA, a process algebra for the modelling and the analysis of biochemical networks. It is a modification of PEPA, originally defined for the performance analysis of computer systems, in order to handle some features of biological models, such as stoichiometry and the use of general kinetic laws. The domain of application is the one of biochemical networks. Bio-PEPA may be seen as an intermediate, formal, compositional representation of biological systems, on which different kinds of analysis can be carried out. Bio-PEPA is enriched with some notions of equivalence. Specifically, the isomorphism and strong bisimulation for PEPA have been considered. Finally, we show the translation of three biological models into the new language and we report some analysis results.

We study syntax-free models for name-passing processes. For interleaving semantics, we identify the indexing structure required of an early labelled transition system to support the usual pi-calculus operations, defining Indexed Labelled Transition Systems. For noninterleaving causal semantics we define Indexed Labelled Asynchronous Transition Systems, smoothly generalizing both our interleaving model and the standard Asynchronous Transition Systems model for CCS-like calculi. In each case we relate a denotational semantics to an operational view, for bisimulation and causal bisimulation respectively. We establish completeness properties of, and adjunctions between, categories of the two models. Alternative indexing structures and possible applications are also discussed. These are first steps towards a uniform understanding of the semantics and operations of name-passing calculi.

Abstract. We study properties of asynchronous communication independently of any concrete concurrent process paradigm. We give a general-purpose, mathematically rigorous definition of several notions of asynchrony in a natural setting where an agent is asynchronous if its input and/or output is filtered through a buffer or a queue, possibly with feedback. In a series of theorems, we give necessary and sufficient conditions for each of these notions in the form of simple first-order or second-order axioms. We illustrate the formalism by applying it to asynchronous CCS and the core join calculus.