Fundamentals of Software Architecture, 2nd Edition

Chapter 3. Modularity

Architects and developers have struggled with the concept of modularity for quite some time, as is evident in this quote from Composite/Structured Design (Van Nostrand Reinhold, 1978):

95% of the words [written about software architecture] are spent extolling the benefits of “modularity” and little, if anything, is said about how to achieve it.

Glenford J. Myers

Different platforms offer different reuse mechanisms for code, but all support some way of grouping related code together into modules. While this concept is universal in software architecture, it has proven slippery to define. A casual internet search yields dozens of definitions, with no consistency (and some contradictions). This isn’t a new problem. However, because no recognized definition exists, we must jump into the fray and provide our own definitions for the sake of consistency throughout the book.

Understanding modularity and its many incarnations in the development platform of choice is critical for architects. Many of the tools we have to analyze architecture (such as metrics, fitness functions, and visualizations) rely on modularity and related concepts. Modularity is an organizing principle. If an architect designs a system without paying attention to how the pieces wire together, that system will present myriad difficulties. To use a physics analogy, software systems model complex systems, which tend toward entropy (or disorder). In a physical system, energy must be added to preserve ...