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Chapter 6. Change Dynamics
We also gather the following statistics by comparing a version with the
previous version in the release history (if a previous version if available):
u v
c v
a v
ratio of classes that are unchanged
ratio of classes that are changed
ratio of classes that are added
The percentages u v , c v , and a v are determined as follows:
u v = |U v|
|N v |
(6.2.5)
c v = |C v|
|N v |
(6.2.6)
a v = |A v|
|N v |
(6.2.7)
and,
u v + c v + a v = 1 (6.2.8)
In our input data set, we determined that for any given version v, the
following property (Equation 6.2.9) holds in 80% of the versions:
u f v > c f v > d f v (6.2.9)
and the following property (Equation 6.2.10) holds for 75% of versions:
u v > c v > a v (6.2.10)
When we look ahead one version, on average across all systems that we
studied, we observe that 75% of the classes are unchanged, 20% are
modified and 5% are removed. When we look back one version to detect
new classes, on average we note that 70% of the classes are unchanged,
22% are modified and around 8% are new classes. Figure 6.2 highlights
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