Abstracting Interaction Patterns : A Programming Paradigm for OpenDistributed

ing Interaction Patterns: A Programming Paradigm for Open Distributed Systems Gul A. Agha Open Systems Laboratory Department of Computer Science, 1304 W. Spring eld Avenue, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA, Email: [email protected], 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 speci cation 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 de ne actors as a model of concurrency for open systems. We then review a number of programming abstractions that are useful in modular speci cation and implementation of open systems. Such abstractions include activators, protocols, synchronizers, and actorspaces. We observe that de ning such abstractions for complex interaction patterns requires a sort of system decomposition that is not supported by standard execution models of concurrent programming, including actors and process algebras. Rather, a suitable meta-architecture is needed to allow the implementation of abstract representations of interaction patterns. Currently there is no entirely satisfactory formal theory of meta-architectures.