A Standard Description of the Terms Module and Modularity for Systems Engineering

The terms module and modularity are not part of the technical taxonomy in any of the systems engineering standards, which do not regard a module as a part of the formal system breakdown structure. In this paper, we redefine the term module as a unit composed of a set of components with a set of specific interfaces. This unit serves one or more purely nonfunctional goals, such as flexibility, evolvability, manufacturability, testability, and maintainability. According to this definition, a configuration item, a subsystem, an assembly, a subassembly, or a component can all be regarded as modules as they can serve nonfunctional goals. The important assertion here is that a module's boundaries do not necessarily coincide with those dictated by the functional or spatial system decomposition and hierarchy. The aim of this paper is to lay the foundations for the future standardization of various engineering design processes based on modularity for nonfunctional benefits. A clear definition of the terms module and modularity can assist systems designers and developers to optimize the value of a modular system. This research highlights the present inconsistencies in the field of modular system design and puts forward some critical questions, which will shape the future research into this field.