Software architectures shift developers' focus from lines-of-code to coarser-grained architectural elements and their interconnection structure. Architecture description languages (ADLs) have been proposed as modeling notations to support architecture-based development. There is, however, little consensus in the research community on what is an ADL, what aspects of an architecture should be modeled in an ADL, and which ADL is best suited for a particular problem. Furthermore, the distinction is

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... rarely made between ADLs on one hand and formal specification, module interconnection, simulation, and programming languages on the other. This paper attempts to provide an answer to these questions. It motivates and presents a definition and a classification framework for ADLs. The utility of the definition is demonstrated by using it to differentiate ADLs from other modeling notations. The framework is used to classify and compare several existing ADL~.' * Although ACME is not an ADL, it contains a number of ADL-like features. We include it in the paper in order to highlight the difference between an ADL and an interchange language. Due to space constraints, details of these approaches are omitted. They are provided in [Med97] .