Customization and composition of distributed objects: middleware abstractions for policy management

Current middleware solutions such as CORBA and Java's RMI emphasize compositional design by separating functional aspects of a system (e.g. objects) from the mechanisms used for interaction (e.g. remote procedure call through stubs and skeletons). While this is an effective solution for handling distributed interactions, higher-level requirements such as heterogeneity, availability, and adaptability require policies for resource management as well as interaction. We describe the Distributed Connection Language (dcl): an architecture description language based on the Actor model of distributed objects. System components and the policies which govern an architecture are specified as encapsulated groups of actors. Composition operators are used to build connections between components as well as customize their behavior. This customization is realized using a meta-architecture. We describe the syntax and semantics of dcl, and illustrate the language by way of several examples.