thesis - Faculty of Information and Communication Technologies ...

Chapter 6. Change Dynamics
abstract classes or enum declarations. The typical zero distance change
in these classes involves modifications such as reordering of parameters
in method signatures, renaming fields, parameters or methods, as
well as changes to type names (return types or dependent types).
In all of the systems that we studied, we have not found an instance
where all 54 metrics have changed. The maximum that we found was
34 changed metric values. However, the set of changed metrics was
different for different classes and systems.
6.2.4 Modified Classes and Popularity
In the previous sections we addressed the probability, frequency and
distribution of change. But, what characterizes the classes that do
change? In particular, does popularity increase the stability of a class?
In order to answer this question, within every release across all systems
in our data set we analysed the proportion of classes that are popular
p v (Equation 6.2.11), against the proportion of all the popular classes
that are modified cv p (Equation 6.2.12). In the following two equations,
Nv p is the set of popular classes, Cv p is the set of popular classes that are
modified, and N v is the set of classes in version v.
p v = |N p v |
|N v |
(6.2.11)
c p v = |Cp v |
|C v |
(6.2.12)
In order to ensure sufficient statistical power (in terms of our ability
to compare both samples), we eliminate releases where less than 30
classes have changed [271] (Chapter1). Approximately 20% of the releases
in our data set have less than 30 modified classes and these have
been excluded from our data analysis.
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