Modules In Object-Oriented Systems

This paper discusses aspects of modularity in object-oriented systems. We substantiate the need for components that are less fine-grained than classes. We propose to use subsystems in design and modules in specification and implementation to encapsulate cooperating classes. Such larger components are better comprehensible and reusable than single classes can be. We present precise criteria that modules have to fulfil, ensuring modules to be self-contained. This supports incremental software development: a module being added to a software library, its specified properties cannot be invalidated by other components. Also, we discuss how several modules relate to one another and introduce a compatibility relationship between modules.