thesis - Faculty of Information and Communication Technologies ...

Chapter 5. Growth Dynamics
as existing classes gain more size and complexity, that is, they become
relatively wealthier.
In our data set, we found a generalizable and consistent trend only in
the Gini Coefficient for In-Degree Count. The Gini Coefficients for all
other metrics increase in some systems, while in others they decrease.
Our finding shows that the change in distribution of class size and
structural complexity is not a consistent and predictable evolutionary
property. The variability in the Gini coefficients across systems suggests
that there are different evolutionary pressures for different systems
and developers respond as needed. However, the stability of the
distribution profiles indicates that a system generally keeps its character
over time — a finding that provides some indirect support for the
Law of Conservation of Familiarity (cf. Section 2.3).
When developers add a set of new classes, these fit within the overall
probability distribution profile as indicated by the minimal change in
the Gini coefficient. Although our observations indicate that the longterm
trend for most Gini Coefficient values cannot be reliably predicted,
there is a high probability that the distribution of size and complexity
between any two consecutive versions are very similar.
5.5.3 Preferential Attachment
We analyzed the trend in the Gini values to answer one of our research
questions – “do large and complex classes get bigger over time?”. If large
and complex classes gain additional volume in terms of code, then they
will grow at a slightly faster rate than the rest of the code base causing
the Gini Coefficient values to increase as software evolves. Our observations
showed a consistent trend in the Gini Coefficient value of IDC,
but none of the other metrics had a sufficiently generalizable trend.
In some systems there was an increase, while in others there was a
decrease in the Gini Coefficient values over time.
Our findings show that popular classes tend to gain additional dependents
indicating that, in general, software systems are built incre-
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