Algebraic specification of modules and configuration families

Modular software systems usually evolve during a longer period of time, in which several versions of single modules and system parts exist. Module families and configuration families as introduced here provide a theoretical background in which module specifications, interface specifications and system interconnections together with their relationship w.r.t. different development steps can be described precisely. Module and interface specifications are collections of algebraic specifications. Both may be structured using operations like composition, union and actualization. This structure establishes the system interconnections. Development in time is modelled by the notions of refinement and realization. Module and interface specifications can be refined separately. Both development phases are connected via some realization steps relating interfaces to modules that satisfy the corresponding interface specification. Development in time that does not change the system interconnection is compatible with this structure, i.e. correct development steps of the parts induce a correct development step of the whole system. As an example the authors develop in several steps the modular specification of a desk calculator, enhancing the original specification by additional features.