Class Responsibility (CR)

Overview

The Class Responsibility metric provides the degree of responsibility of a class or a package.

For a class (and respectively for a package), it gives the percentage of operations that include pre or post-conditions, with regard to the number of operations that the class (and respectively the package) has.

Computation

The ... variable	represents the …
PCC	number of operations which implement pre-condition contracts
POC	number of operations which implement post-condition contracts
NOM	number of operations

Nominal range

Between 20 % and 75 %

Analysis

The application is more robust if classes check the conditions of use for their services and their returned results. However, too many checks can introduce a certain encumbrance which is not necessarily needed.

The fewer pre and post-conditions there are on the operations of a class, the more the class will be similar to a group of functions, rather than a consistent set of operations.

The robustness and the re-use of components which use pre and post-conditions will be increased.

Certain operations that only read attributes will not have pre and post-conditions. This explains why the upper limit of 100% is very rarely reached.

A value of less than 20% is more alarming than a value greater than 75%.