Software Architecture in Practice, Third Edition

7. Modifiability

Adapt or perish, now as ever, is nature’s inexorable imperative.

—H.G. Wells

Change happens.

Study after study shows that most of the cost of the typical software system occurs after it has been initially released. If change is the only constant in the universe, then software change is not only constant but ubiquitous. Changes happen to add new features, to change or even retire old ones. Changes happen to fix defects, tighten security, or improve performance. Changes happen to enhance the user’s experience. Changes happen to embrace new technology, new platforms, new protocols, new standards. Changes happen to make systems work together, even if they were never designed to do so.

Modifiability is about change, and our interest ...