An interaction calculus for concurrent systems

Lecture Notes in Computer Science, 1997

We present a new type system for TyCO, a name-passing calculus of concurrent objects. The system captures dynamic aspects of the behaviour of objects, namely non-uniform service availability. The notion of processes without errors is loosened, demanding only weak fairness in the treatment of messages.

1996

Abstract. We propose Interaction Categories as a new paradigm for tinsemantics of functional and concurrent computation. Interaction categories have specifications as objects, processes as morphisms, and interaction as composition. We introduce two key examples of interaction categories for concurrent computation and indicate how a general axiomatisation can be developed.

Lecture Notes in Computer Science, 1989

FACILE is a language which symmetrically integrates concurrent and functional programming. It is a typed and statically scoped language. The language supports both function and process abstractions.

In this paper we present an operational semantics for concurrent interactive process es in the purely functional programming language Clean. An interactive process is in essence a state transition system which apart from its logical state can also access the state of the file system, do highlevel Graphical User I/O, and do inter-process communication via synchronous and asynchronous message passing and data sharing. Inter-process communication is type-safe and polymorphic. The semantics of the system is based on earlier work on the Interleaved Event I/O system. In this paper we identify limitations of the interleaved model in the context of concurrent processes and propose a new process semantics that does allow a concurrent implementation. The method basically intro duces a Remote Procedure Call communication scheme and demonstrates how to apply this scheme to obtain a concurrent process semantics. The resulting system is the Concur rent Event I/O system . The operational semantics is given in Clean itself. As a result the concurrency system is completely func tional because the construction is done within the pure functional framework.

Software: Practice and Experience, 1992

LOTOS is one of the most recent formal description languages to appear and one of very few with a standard definition. It has both a process algebra and an abstract data-type component, and these facilities are used in combination to describe the behaviour of concurrent systems. The purpose of this paper is to examine, in a tutorial style, what is involved in constructing and taking benefit from such descriptions. The presentation is illustrated through the development of two formal descriptions for the children's game of pass-the-parcel. These descriptions and a concise summary of the main features of LOTOS are given as appendices. Many of the points made in the paper apply equally well to other process-oriented languages such as CCS and CSP.

Algebraic Foundations of Systems Specification, 1999

This article presents an extension of the formalism of algebraic specifications to the specification of concurrent systems. The key concept is that of process specifications, which have two hierarchical layers: processes and data. Processes apply to data via an application operator, eventually yielding a set of data as a result. Syntax and semantics of process specifications are presented, with emphasis on methodological issues (how to write hierarchically consistent and complete specifications). A suitable notion of observational congruence is introduced and characterized. A notion of implementation is denned, and a general method for proving correction is considered, based on the notion of serializability proof. A primitive for putting specifications together, in parellel, is analyzed. Finally, richer primitives for building basic specifications are discussed. Our proposal is illustrated via several examples inciuding the one of the systematic, stepwise development of a complex specification. * Partially supported by the Esprit 432 METEOR project.

Electronic Notes in Theoretical Computer Science

λS extends the λ-calculus with recursive bindings, barriers, and updatable memory cells with synchronized operations. The calculus can express both deterministic and nondeterministic computations. It is designed to be useful for reasoning about compiler optimizations and thus allows reductions anywhere, even inside λ's. Despite the presence of side effects, the calculus retains fine-grained, implicit parallelism and non-strict functions: there is no global, sequentializing store. Barriers, for sequencing, capture a robust notion of termination. Although λS was developed as a foundation for the parallel functional languages pH and Id, we believe that barriers give it wider applicability — to sequential, explicitly parallel and concurrent languages. In this paper we describe the λS-calculus and its properties, based on a notion of observable information in a term. We also describe reduction strategies to compute maximal observable information even in the presence of unbounded nond...

2002

the modelling of mobile processes is not straightfor-DARWIN is a configuration language f o r distributed and parallel programs, providing a hierarchical structure of components with dynamic binding. In order t o specify precisely the behaviour of DARWIN programs, we sketch a translation of the features of the language into the a-calculus, a formalism for modelling concurrent processes. The match between underlying models f o r DARWIN and ?r-calculus is good. Examples done in the calculus are clean abstractions of the same solutions in other concurrent languages.

Information and Control

Theoretical Computer Science, 2004

Concurrent computation can be given an abstract mathematical treatment very similar to that provided for sequential computation by domain theory and denotational semantics of Scott and Strachey. A simple domain theory for concurrency is presented. Based on a categorical model of linear logic and associated comonads, it highlights the role of linearity in concurrent computation. Two choices of comonad yield two expressive metalanguages for higher-order processes, both arising from canonical constructions in the model. Their denotational semantics are fully abstract with respect to contextual equivalence. One language, called HOPLA for Higher-Order Process LAnguage, derives from an exponential of linear logic. It can be viewed as an extension of the simply-typed lambda calculus with CCS-like nondeterministic sum and prefix operations, in which types express the form of computation path of which a process is capable. HOPLA can directly encode calculi like CCS, CCS with process passing, and mobile ambients with public names, and it can be given a straightforward operational semantics supporting a standard bisimulation congruence. The denotational and operational semantics are related with simple proofs of soundness and adequacy. Full abstraction implies that contextual equivalence coincides with logical equivalence for a fragment of Hennessy-Milner logic, linking up with simulation equivalence. The other language is called Affine HOPLA and is based on a weakening comonad that yields a model of affine-linear logic. This language adds to HOPLA an interesting tensor operation at the price of linearity constraints on the occurrences of variables. The tensor can be understood as a juxtaposition of independent processes, and allows Affine HOPLA to encode processes of the kind found in treatments of nondeterministic dataflow. The domain theory can be generalised to presheaf models, providing a more refined treatment of nondeterministic branching and supporting notions of bisimulation. The operational semantics for HOPLA is guided by the idea that derivations of transitions in the operational semantics should correspond to elements of the presheaf denotations. Similar guidelines lead to an operational semantics for the first-order fragment of Affine HOPLA. An extension of the operational semantics to the full language is based on a stable denotational semantics which associates to each computation the minimal input necessary for it. Such a semantics is provided, based on event structures; it agrees with the presheaf semantics at first order and exposes the tensor operation as a simple parallel composition of event structures. The categorical model obtained from presheaves is very rich in structure and points towards more expressive languages than HOPLA and Affine HOPLA-in particular concerning extensions to cover independence models. The thesis concludes with a discussion of related work towards a fully fledged domain theory for concurrency. v Thanks to my supervisor, Glynn Winskel, for four years of joint work under his expert leadership-and for introducing me to some of the good things in life besides research, like Jalfrezi and Habit Ale; my committee members Pierre-Louis Curien and Guy McCusker for their thoughtful and detailed comments, corrections and suggestions for improving the thesis; Pino Rosolini and the people at DISI, University of Genoa, for their hospitality during my stay there and for helpful comments on my work-and especially to Matías Menni for his friendship; Marcelo Fiore for his insightful suggestions at my Part A exam; Erik Meineche Schmidt and Mogens Nielsen for their early encouragement; the staff and students at Daimi/BRICS for creating a stimulating working environment; "Laesegruppen" and "Frokostklubben" for forcing me to have a life besides my studies (or, at least for trying); my family for boldly asking questions about my research even though my answers were often incomprehensible. Last, but certainly not least, I wish to thank my wife Mette for her support, her patience, and her unwavering faith in me.