Method Invocation Coupling (MIC)

Description:

MIC is the (relative) number of other classes to which a certain class sends messages.

MIC_norm = n_MIC/(N -1)

where N is the total number of classes defined in the project, and n_MIC the number of classes to which messages are sent.

Viewpoints. These viewpoints summarize the impact that coupling has on some external attributes.

1. Maintainability. The maintenance of a strongly coupled class (high MIC value) is more difficult to do because of its dependency on the classes it is coupled to.
2. Comprehensibility. A strongly coupled class is more difficult to understand, as its understanding implies a partial (or sometimes total) understanding of the classes it is coupled to.
3. Error-prone and Testability. Errors in a class is directly proportional to the number of couplings to other classes. Consequently high coupling has a negative impact on testability.

Observations

1. The proposed definition of MIC is obviously a normalized one. Although this has advantages, but for some viewpoints, like maintainability, it is more important to operate on the absolute values, i.e. the number of classes to which it is coupled.
2. For some viewpoints it might be important to count only the couplings of the system to user-defined classes, i.e. exclude the library classes.

Source: Ing. Radu Marinescu. An Object Oriented Metrics Suite on Coupling. Universitatea "Politehnica" Timisoara, Facultatea de Automatica si Calculatoare, Departamentul de Calculatoare si Inginerie Software. September, 1998.