There is a real need for clear and sound design specifications of distributed systems at the architectural level. This is the level of the design which deals with the high-level organisation of computational elements and the interactions between those elements. The paper presents the Darwin notation for specifying this high-level organisation. Darwin is in essence a declarative binding language which can be used to define hierarchic compositions of interconnected components. Distribution is dealt with orthogonally to system structuring. The language supports the specification of both static structures and dynamic structures which may evolve during execution. The central abstractions managed by Darwin are components and services. Services are the means by which components interact. In addition to its use in specifying the architecture of a distributed system, Darwin has an operational semantics for the elaboration of specifications such that they may be used at runtime to di...

Much of the recent work on Architecture Description Languages (ADL) has concentrated on specifying organisations of components and connectors which are static. When the ADL specification is used to drive system construction, then the structure of the resulting system in terms of its component instances and their interconnection is fixed. This paper examines ADL features which permit the description of dynamic software architectures in which the organisation of components and connectors may change during system execution. The paper outlines examples of language features which support dynamic structure. These examples are taken from Darwin, a language used to describe distributed system structure. An operational semantics for these features is presented in the n-calculus, together with a discussion of their advantages and limitations. The paper discusses some general approaches to dynamic architecture description suggested by these examples. 1

The paper addresses the problem of structuring and managing large distributed systems constructed from many distributed objects. Specifically, the paper proposes a component model which can be used to compose objects into manageable entities. Components are specified using Darwin, an architecture description language developed by the authors. A mapping of distributed objects into Darwin components is described together with an outline of how Darwin and its associated tools are implemented in a CORBA compliant environment. keywords: distributed software architecture, components, object management 1. Introduction A recent study in software maintenance for distributed systems [12] has indicated that the move to distribution has contributed to the simplification of primitive software components in a distributed architecture. However, this benefit is often overwhelmed by the increased complexity of the overall distributed system and its architecture. The architectural description language ...