thesis - Faculty of Information and Communication Technologies ...

Chapter 5. Growth Dynamics
(see Figure 5.13 showing the Number of Branches Gini Coefficient values
for JabRef). JabRef is a tool that helps manage bibliography databases,
specifically BibTex files. Interestingly, the developers initially used a
hand-written parsers and in RSN 6 introduced a machine generated
parser. The introduction of the machine generated parser for BibTex
files caused the Number of Branches Gini Coefficient value to increase
from 0.74 to approximately 0.91 (see Figure 5.13).
High Gini Coefficient values indicate that these systems have a small
set of very large and complex classes (wealthy in terms of size and complexity).
As noted earlier, human developers rarely write code in which
Gini Coefficients for specific measures go past 0.80 as they will find it
hard to write and maintain methods with very high algorithmic complexity
[74,263]. The ability of detecting and flagging machine generated
code is valuable since it signals the possible need for additional expertise
in order to maintain or enhance an existing code base and to meet
strategic objectives.
Interestingly, we did notice a higher Number of Branches value (Gini Coefficient
around 0.8) in two XML parsers Xerces and Xalan, both of which
contained human written parsers. We determined that they were hand
written by studying repository access logs and comments left within
the code. When machines generate parsers, they create a full set of
classes rather than partially adjusting a few lines to fix defects, this is
visible in the repository logs related to those files. Further, the code
files written by machine use variable names that are alpha-numeric
with the numeric component increasing in value for each new variable
rather than in a human readable form (for example the variables generated
by the machine generated parser take the form jj_123, jj_124,
jj_125 etc.)
Surprisingly, in software with human written parsers, the developers
choose to centralise the functionality of the parser into a few classes
with large and complex methods rather than distributing the complexity
among a large number of classes. Though these classes did not match
the size or complexity of machine generated code, they influenced the
overall distribution sufficiently to cause a higher Gini value.
135