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...ir interrelationships, and principles and guidelines governing their design and evolution over time [8]. It is a critical design concern when bridging the gap between requirements and implementations =-=[7,8,9,10,25,28]-=-. Architectural Description Languages (ADLs) are notations for expressing and representing architectural designs and styles. They describe the high level structure of a system in terms of components a...

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...the deletion of both components and bindings created by a previous specification. Previous work has identified an approach which minimises the disruption to a system while such change is accomplished =-=[14]-=-. This metalevel approach has been used in a prototype management system for distributed applications [6] in which the configuration manager is essentially a Darwin interpreter. This configuration man...

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...date, much of this work has concentrated on providing precise descriptions of connectors which provide the "glue" for combining components into systems[9,10] and accommodating diverse connector types =-=[2,28]-=-. As exemplified by UniCon[28], they Permission to make digital/hard copy of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distribu...

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...ation can be used in a way which balances flexibility at run-time with the advantages of retaining a structural description. Figure 5 is an example taken from an infrared Active Badge location system =-=[11]-=- implemented using Darwin and Regis [19]. The comexec component forms part of the badge management server which runs on a local area network and uses a set of fixed infrared tranceivers to communicate...

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...raction - facilitates the provision of an operational semantics for Darwin as a "pure" structural language. We avoid consideration of the interactions (cf. connectors [2]) and/or components (cf. CHAM =-=[12]-=- or LTS [4] models), but focus on services and binding. This does not preclude specification of the interaction and/or computation, but allows us to modularise our approach. This focus is matched by t...

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...ir interrelationships, and principles and guidelines governing their design and evolution over time [8]. It is a critical design concern when bridging the gap between requirements and implementations =-=[7,8,9,10,25,28]-=-. Architectural Description Languages (ADLs) are notations for expressing and representing architectural designs and styles. They describe the high level structure of a system in terms of components a...

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...ough the description of generic software architectures which can be elaborated and instantiated to form specific executable architectures. It is currently being used in the context of the Regis system=-=[19]-=- which supports multiple interaction primitives and in the Sysman project[6] with CORBA[29] which uses remote object invocation for component interaction. Darwin's declarative property has facilitated...

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... languages have much in common with ADLs in describing a system as a configuration of connected component instances. They differ mainly in restricting connectors to those compatible with distribution =-=[3,26]-=-. Darwin, the latest in a line of configuration languages, is a declarative language which is intended to be a general purpose notation for specifying the structure of distributed systems composed fro...

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...30]. Constraints did not play a part in the construction of a system from its architectural specification, however they were used to ensure that implementations conformed to their specification as in =-=[23]-=-. Others, such as the Raven configuration management system [5], have shown that constraints can be useful for recognising valid structures and for performing repairs. In conclusion... This paper has ...

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... reconfiguration events. These reconfiguration events capture the imperative quality of change while the system specification remains declarative. Others, such as the reconfiguration plans of Clipper =-=[1]-=- and the reconfiguration actions of Durra [3], describe a similar use of imperative commands in response to system events, though with less support for maintaining the integrity of the system than tha...

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... Darwin to capture dynamic structures, lazy instantiation and direct dynamic instantiation. In addition, dynamic binding is discussed with respect to open systems and abstract services. The r~calculus=-=[21]-=- is used to specify these dynamic constructs. This builds on earlier work which developed a n-calculus model for the static aspects of Darwin and demonstrated the correctness of the elaboration of Dar...

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...ages of type int. Darwin does not interpret service type information. Service type information is either interpreted by the underlying behaviour specification formalism used during design and analysis=-=[4]-=- or, as in the example, denotes a communication mechanism supported by the underlying distributed platform used in building an implementation. In the Regis system[19], this information is used to dire...

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...stem from its architectural specification, however they were used to ensure that implementations conformed to their specification as in [23]. Others, such as the Raven configuration management system =-=[5]-=-, have shown that constraints can be useful for recognising valid structures and for performing repairs. In conclusion... This paper has described our approach and the associated rationale for using a...

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...tion mechanisms. It deliberately divides the description of structure from that of computation and interaction in order to provide a clear separation of concerns. Darwin supports software composition =-=[24]-=- through the description of generic software architectures which can be elaborated and instantiated to form specific executable architectures. It is currently being used in the context of the Regis sy...

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...d and instantiated to form specific executable architectures. It is currently being used in the context of the Regis system[19] which supports multiple interaction primitives and in the Sysman project=-=[6]-=- with CORBA[29] which uses remote object invocation for component interaction. Darwin's declarative property has facilitated the provision of an operational semantics and the ability to reason about s...

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...one which closely models the current Darwin implementation, is to give service names a structure and encode the lazy property in this structure. This can easily be achieved in the polyadic r~-calculus=-=[22]-=- but it is beyond the scope of this paper. The combination of lazy instantiation and recursion can be used to describe a wide range of commonly occurring distributed parallel processing structures (e....