Architectural specifications in CASL

. One of the novel features of Casl, the Common Algebraic Specification Language, is the provision of so-called architectural specifications for describing the modular structure of software systems. A discussion of refinement of Casl specifications provides the setting for a presentation of the rationale behind architectural specifications. This is followed by details of the features provided in Casl for architectural specifications, hints concerning their semantics, and simple results justifying their usefulness in the development process. 1 Introduction A common feature of present-day algebraic specification languages (see e.g. [SW83], [EM85], [GH93], [CoFI96], [SW98]) is the provision of specificationbuilding operations [BG77] for building large specifications in a structured fashion from smaller and simpler ones. Less usual are features for describing the modular structure of software systems under development. This paper is about the facilities for this that are provided in Casl..