Software package metrics

Various software package metrics are used in <a href="/facts/Modular_programming/sNoqKvRD">modular programming</a>. They have been mentioned by <a href="/facts/Robert_Cecil_Martin/JBbAPbfr">Robert Cecil Martin</a> in his 2002 book Agile software development: principles, patterns, and practices.
The term <a href="/facts/Package_manager/kEX4kx7g">software package</a> here refers to a group of related <a href="/facts/Class_(computer_science)/zvzkSAtE">classes</a> in <a href="/facts/Object-oriented_programming/TxNMEcao">object-oriented programming</a>.

<ul><li>Number of classes and interfaces: The number of concrete and abstract classes (and interfaces) in the package is an indicator of the extensibility of the package.</li>
<li><a href="/facts/Coupling_(computer_programming)/QEeSaXF3">Afferent couplings</a> (Ca): The number of classes in other packages that depend upon classes within the package is an indicator of the package's responsibility. <a href="/facts/Afferent_couplings/766AT8qD">Afferent couplings</a> signal inward.</li>
<li><a href="/facts/Efferent_coupling/U7uPVCyx">Efferent couplings</a> (Ce): The number of classes in other packages that the classes in a package depend upon is an indicator of the package's dependence on <a href="/facts/Externality/hGgw7gtT">externalities</a>. Efferent couplings signal outward.</li>
<li>Abstractness (A): The ratio of the number of abstract classes (and interfaces) in the analyzed package to the total number of classes in the analyzed package. The range for this metric is 0 to 1, with A=0 indicating a completely concrete package and A=1 indicating a completely abstract package.</li>
<li>Instability (I): The ratio of efferent coupling (Ce) to total coupling (Ce + Ca) such that I = Ce / (Ce + Ca). This metric is an indicator of the package's resilience to change. The range for this metric is 0 to 1, with I=0 indicating a completely stable package and I=1 indicating a completely unstable package.</li>
<li>Distance from the main sequence (D): The perpendicular distance of a package from the idealized line A + I = 1. D is calculated as D = | A + I - 1 |. This metric is an indicator of the package's balance between abstractness and stability. A package squarely on the main sequence is optimally balanced with respect to its abstractness and stability. Ideal packages are either completely abstract and stable (I=0, A=1) or completely concrete and unstable (I=1, A=0). The range for this metric is 0 to 1, with D=0 indicating a package that is coincident with the main sequence and D=1 indicating a package that is as far from the main sequence as possible.</li>
<li>Package dependency cycles: Package dependency cycles are reported along with the hierarchical paths of packages participating in package dependency cycles.</li></ul>

Software package metrics open-in-new

Software package metrics