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The deep symmetry of Linear Logic [18] makes it suitable for providing abstract models of computation, free from implementation details which are, by nature, oriented and non symmetrical. I propose here one such model, in the area of Logic Programming, where the basic computational principle is Computation = Proof search.

Polyphonic C# is an extension of the C# language with new asynchronous concurrency constructs, based on the join calculus. We describe the design and implementation of the language and give examples of its use in addressing a range of concurrent programming problems.

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Machines Jean-Marc Andreoli, Paolo Ciancarini and Remo Pareschi European Computer Industry Research Centre Abstract In this paper, we introduce the metaphor of Interaction Abstract Machines (IAMs), in the same vein of such metaphors as the Chemical Abstract Machine. The main point about IAMs is in allowing interactions among independent, locally defined subsystems --- a crucial requirement for capturing the global behavior of open systems. IAMs amalgamate dual concepts in distributed problem solving, such as blackboards and broadcast communication, which are exploited to account for, respectively, the tight integration and the loose integration of system components. The formal counterpart for the IAM metaphor can be found in the computational model of Linear Objects (LO), whose aim is the abstract modeling of concurrent agent-oriented computations and whose operational semantics is given in terms of the proof theory of Linear Logic, a framework recently introduced to provide a theoretical account for the notion of (inter)action.

s are available from the same host in the directory /pub/TR/UBLCS/ABSTRACTS in plain text format. All local authors can be reached via e-mail at the address last-name@cs.unibo.it. UBLCS Technical Report Series 92-1 Mapping Parallel Computations onto Distributed Systems in Paralex, by O. Babao glu, L. Alvisi, A. Amoroso and R. Davoli, January 1992. 92-2 Parallel Scientific Computing in Distributed Systems: The Paralex Approach, by L. Alvisi, A. Amoroso, O. Babao glu, A. Baronio, R. Davoli and L. A. Giachini, February 1992. 92-3 Run-time Support for Dynamic Load Balancing and Debugging in Paralex, by O. Babao glu, L. Alvisi, S. Amoroso, R. Davoli, L. A. Giachini, September 1992. 92-4 Paralex: An Environment for Parallel Programming in Distributed Systems, by O. Babao glu, L. Alvisi, S. Amoroso, R. Davoli, L. A. Giachini, October 1992. 93-1 Consistent Global States of Distributed Systems: Fundamental Concepts and Mechanism, by O. Babao glu and K. Marzullo, January 1993. 93-2 Understand...

... This paper reviews most of the work done by various groups along these lines and the current perspectives of our own research on Gamma. For the sake of clarity we separate the contributions in three categories: (1) the relevance of the chemical reaction model for software engineering, (2) extensions of the original model and (3) implementation issues.

1 Introduction In the beginning of constraint logic programming (CLP), constraint solving was "hard-wired " in a built-in constraint solver written in a low-level language. While efficient, this so-called "black-box " approach makes it hard to modify a solver or build a solver over a new domain, let alone debug, reason about and analyze it. This is a problem, since one lesson learned from practical applications is that constraints are often heterogeneous and application-specific. Consequently, several proposals have been made to allow more for flexibility and customization of constraint systems ("glass-box " or even "no-box " approaches):- Demons, forward rules and conditionals in CHIP [6] allow the definition of

Abstract not found

With the growing complexity of software, incurred by the widespread acceptance of parallel and distributed computer systems and networks, program design would benefit from clearly separating the correctness issues (the computation) from efficiency issues (the coordination). Gamma has shown to be a powerful and expressive programming model that allows the basic computations of a program to be expressed with a minimum of control. This enables the programmer to defer efficiency related decisions until a second stage in the design process. In support of this second activity we introduce in this paper a coordination language that exploits the highly nondeterministic behaviour of Gamma to impose additional control. Furthermore, we propose a compositional notion of refinement that can be used to reason about coordination of Gamma programs. This notion induces a number of refinement laws that can be used in an algebraic style of reasoning. Some examples are presented to illustrate application ...