An Implementation - Oriented Semanticsfor Module Composition

This paper describes an approach to module composition by executing \module expressions" to build systems out of component modules. This approach extends the structural description capabilities of existing Architecture Description Languages (ADLs) to facilitate the manipulation of architectural components in a manner that results in either new components or complete instantiations of parameterized architectures. The paper also gives a novel semantics intended to aid with the implementation this approach. The semantics is based on set theory, and uses the technical notions of tuple set, partial signature, and institution, avoiding more diicult mathematics such as abstract algebra and category theory. Language features include information hiding, both vertical and horizontal composition, and views for binding modules to interfaces. Vertical composition refers to the hierarchical structuring of a system into layers, while horizontal composition refers to the structure of a given layer. Modules may involve information hiding, and views may involve behavioral satisfaction of a theory by a module. Finally, this paper includes a number of \Laws of Software Composition" that show how the various module composition operations are related.