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Chapter 3. Data Selection Methodology
volume to the size measure and have the potential to distort the evolutionary
patterns and may indicate a faster rate of growth than would
be possible if only the contributions of the core team are considered.
Including the external libraries also has the potential to distort measures
of complexity and may indicate that a project is far more complex
than it really is. For example, if a project makes use of two complex
libraries for visualization and signal processing the structural and algorithm
complexity of these libraries will be considered to be part of
the actual project under investigation and the core project will show far
more complexity than what needs to be considered by the developers.
Although, including third party libraries provide another dimension
into evolution, from the developers perspective the effort is expended
on selection of the library and learning it rather than in construction of
the library. Furthermore, it is possible that even though a large library
is included, only a small fraction of the features are directly used and
as a consequence reduce the strength of any inferences derived from
the observed evolution. We therefore focus on the set of code that can
be considered to be directly contributed by the developers and hence
potentially maintained by the development team as it evolves.
All systems that we have analyzed made extensive use of additional
Java-based third party libraries with a few systems making use of libraries
written in C/C++. In our study, these third party libraries as
well as all Java standard libraries are treated as external to the software
system under investigation and for this reason we do not collect
metric data for classes in these libraries (See Figure 3.1). For instance,
if a software system makes extensive use of the Java Encryption API
(provided as part of the standard Java framework), we do not extract
metrics for classes in this external encryption library as the effort that
has gone into developing these libraries does not directly impact on the
software system under investigation.
We also noticed that many projects rely on the same set of libraries and
frameworks. For example, the Apache Java libraries are extensively
used for String, Math, Image, and XML processing. Though, there are
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