By adding reflexion to the chemical machine of Berry and Boudol, we obtain a formal model of concurrency that is consistent with mobility and distribution. Our model provides the foundations of a programming language with functional and object-oriented features. It can also be seen as a process calculus, the join-calculus, which we prove equivalent to the pi-calculus of Milner, Parrow and Walker.

We obtain a new formalism for concurrent object-oriented languages by extending Abadi and Cardelli's imperative object calculus with operators for concurrency from the-calculus and with operators for synchronisation based on mutexes. Our syntax of terms is extremely expressive; in a precise sense it unifies notions of expression, process, store, thread, and configuration. We present a chemical-style reduction semantics, and prove it equivalent to a structural operational semantics. We identify a deterministic fragment that is closed under reduction and show that it includes the imperative object calculus. A collection of type systems for object-oriented constructs is at the heart of Abadi and Cardelli's work. We recast one of Abadi and Cardelli's first-order type systems with object types and subtyping in the setting of our calculus and prove subject reduction. Since our syntax of terms includes both stores and running expressions, we avoid the need to separate store typing from typing of expressions. We translate asynchronous communication channels and the choice-free asynchronous-calculus into our calculus to illustrate its expressiveness; the types of read-only and write-only channels are supertypes of read-write channels.

Applications running on the Internet, or on limited-resource devices, need to be able to adapt to changes in their execution environment at run-time. Current languages and systems fall short of enabling developers to migrate and recon gure application sub-components at program-execution time.

We generate a natural hierarchy of equivalences for asynchronous name-passing process calculi from simple variations on Milner and Sangiorgi's definition of weak barbed bisimulation. The -calculus, used here, and the join calculus are examples of such calculi.

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ing Interaction Patterns: A Programming Paradigm for Open Distributed Systems Gul A. Agha Open Systems Laboratory Department of Computer Science, 1304 W. Springfield Avenue, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA, Email: agha@cs.uiuc.edu, Web: http://www-osl.cs.uiuc.edu To Appear: Formal Methods for Open Object-based Distributed Systems IFIP Transactions, E. Najm and J.-B. Stefani, Editors Chapman & Hall, 1997 Abstract This paper discusses mechanisms addressing the complexity of building and maintaining Open Distributed Systems. It is argued that a new programming paradigm based on modular specification of interaction patterns is required to address the complexity of such systems. Our research is based on developing abstraction mechanisms to simplify the task of developing and maintaining open systems. We define actors as a model of concurrency for open systems. We then review a number of programming abstractions that are useful in modular specification an...

In these notes, we give an overview of the join calculus, its semantics, and its equational theory. The join calculus is a language that models distributed and mobile programming. It is characterized by an explicit notion of locality, a strict adherence to local synchronization, and a direct embedding of the ML programming language. The join calculus is used as the basis for several distributed languages and implementations, such as JoCaml and functional nets.

this paper we consider remote creation, migration, and reachability snapshot services: their specification at different levels of abstraction, and their composition. 1.1 About Actors

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Functional nets combine key ideas of functional programming and Petri nets to yield a simple and general programming notation. They