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Chapter 3. Data Selection Methodology
needed and hence not included during the build process using settings
provided in the Makefile. Hence, when using source code files as input
into a study of evolution, ideally, the build scripts have to be parsed to
determine a the set of files for a specific configuration and then the evolution
of the system for this specific configuration has to be analysed.
Many previous studies [41, 100, 105, 120, 153, 217, 239, 256] that use
release histories do not explicitly indicate if the build scripts have been
pre-processed adequately to ensure that the correct set of source files
is used as the input.
In our study, we use compiled releases (Java classes package inside JAR
files) to construct our release history and so our input data has already
gone through the build process, reducing the chance of encountering
code that is no longer in active use. This approach allows us to focus
on the set of classes that have been deemed fit for release by the
development team.
Third Party Libraries
Development teams in general, use a number of third party Java libraries
as well as the standard Java libraries (which are part of the
Java runtime environment) in order to improve their productivity. In
our study, we classify the set of classes created by the development team
as the core system and focus explicitly on how this core system evolves
(see Figure 3.1). This scope allows us to gain a direct perspective into
the efforts of the development team. Our tighter focus has the advantage
of ensuring that the size and complexity measures that we collect
are not influenced by changes in the external libraries. Although, the
developers of the core system potentially exert some evolutionary pressure
on external libraries as consumers, they do not directly influence
the internal structure, organisation and size of these external libraries.
Our intentional focus of ignoring third party libraries distinguishes our
study from other previous large scale studies into open source software
evolution where this choice was not explicitly made or stated in their
work [39, 120, 129, 188, 217, 239, 306]. These third party libraries add
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