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Current research in specifications is emphasizing the practical use of formal specifications in program design. One way to encourage their use in practice is to provide specification languages that are accessible to both designers and programmers. With this goal in mind, the Larch family of formal specification languages has evolved to support a two-tiered approach to writing specifications. This approach separates the specification of state transformations and programming language dependen-cies from the specification of underlying abstractions. Thus, each member of the Larch family has a subset derived from a programming language and another subset independent of any programming languages. We call the former interface languages, and the latter the Larch Shared Language. This paper focuses on Larch interface language specifications. Through examples, we illustrate some salient features of Larch/CLU, a Larch interface language for the programming language CLU. We give an example of writing an interface specification following the two-tiered approach and discuss in detail issues involved in writing interface specifications and their interaction with their Shared Language components.

Abstract-Software configuration management (SCM) is an emerging discipline. An important aspect of realizing SCM is the task of maintaining the configurations of evolving software systems. In this paper, we provide an approach to resolving some ofthe conceptual and technical problems in maintaining configurations of evolving software systems. The approach provides a formal basis for existing notions of system architecture. The formal properties of this view of configurations provide the underpinnings for a rigorous notion of system integrity, and mechanisms to control the evolution of configurations. This approach is embodied in a language, NuMIL, to describe software system configurations, and a prototype environment to maintain software system configurations. We believe that the approach and the prototype environment offer a firm base to maintain software system configurations and, therefore, to implement SCM. Index Terms-Configuration, module and subsystem families, module and subsystem interfaces, software configuration maintenance system, upward compatibility. I.