Editing Coupling (computer programming) (section)

== Module coupling ==
Coupling in Software Engineering<ref name="Pressman_1982"/> describes a version of metrics associated with this concept.

For data and control flow coupling:

* '''d<sub>i</sub>''': number of input data parameters
* '''c<sub>i</sub>''': number of input control parameters
* '''d<sub>o</sub>''': number of output data parameters
* '''c<sub>o</sub>''': number of output control parameters

For global coupling:

* '''g<sub>d</sub>''': number of global variables used as data
* '''g<sub>c</sub>''': number of global variables used as control

For environmental coupling:

* '''w''': number of modules called (fan-out)
* '''r''': number of modules calling the module under consideration (fan-in)

<math>\mathrm{Coupling}(C) = 1 - \frac{1}{d_{i} + 2\times c_{i} + d_{o} + 2\times c_{o} + g_{d} + 2\times g_{c} + w + r}</math>

<code>Coupling(C)</code> makes the value larger the more coupled the module is. This number ranges from approximately 0.67 (low coupling) to 1.0 (highly coupled)

For example, if a module has only a single input and output data parameter

<math>C = 1 - \frac{1}{1+0+1+0+0+0+1+0} = 1 - \frac{1}{3} = 0.67</math>

If a module has 5 input and output data parameters, an equal number of control parameters, and accesses 10 items of global data, with a fan-in of 3 and a fan-out of 4,

<math>C = 1 - \frac{1}{5 + 2\times 5 + 5 + 2\times 5 + 10 + 0 + 3 + 4} = 0.98</math>