A Simple Model for Reasoning about Limits on Coupling in Object-Oriented Software

Given that all of a program's code must be reachable from its main method, and that type-safety causes this reachability to substantially manifest as compilation dependencies among the program's classes, a simple model for reasoning about limits on coupling among a program's classes—a long-standing question in the software design literature—is proposed. The model takes the form of a directed graph with classes as nodes and four distinct forms of compilation dependencies as labeled edges. As manifested in compilation dependencies, the model suggests that there is a trade-off between direct and transitive coupling, and that certain forms of coupling in a class are prerequisites for the existence of other forms in that same class.