In his influential paper On the Criteria To Be Used in Decomposing Systems into Modules, David L. Parnas offers some simple, timeless advice: if two things change together, they belong together. This is not, in itself, an answer. It simply replaces a nebulous question — do these belong in the same module? — with something more concrete. In this newsletter, we are trying to do something similar. Previously, we established that every change is an explanation. When we say two things are coup...
