Abstract
Coupling of a subsystem characterizes its interdependence with other subsystems. A subsystem's cohesion, on the other hand, characterizes its internal interdependencies. When used in conjunction with other attributes, measurements of a subsystem's coupling and cohesion can contribute to software quality models. An abstraction of a software system can be represented by a graph and a module (subsystem) by a subgraph. Software-design graphs depict components and their relationships. Prior work by Allen and Khoshgoftaar proposed information theory-based measures of coupling and cohesion of a modular system. This paper proposes related information theory-based measures of coupling and cohesion of a module. These measures have the properties of module-level coupling and cohesion defined by Briand, Morasca, and Basili. We define cohesion of a module in terms of intramodule coupling, normalized to between zero and one. We illustrate the measures with example graphs and an empirical analysis of the call graph of a moderate-size C program, the Nethack computer game. Preliminary analysis showed that the information-theory approach has finer discrimination than counting.