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Chapter 3. Data Selection Methodology
Using Binaries
We extract the measures for each class by processing the compiled Java
bytecode instructions generated by the compiler (details are explained
in Chapter 4). This method allows us to avoid running a (sometimes
quite complex) build process for each release under investigation since
we only analyze code that has actually been compiled.
Our approach of using compiled binaries to extract metric data is more
precise when compared to the methods used by other researchers that
studied evolution in open-source software systems since the earlier
work used source code directories as input for their data analysis [41,
100,105,120,153,217,239,256]. In order to process the large amount
of raw data, many of the previous open source software evolution studies
used data gathered from size measures, such as, raw file count,
raw folder count and raw line count. These measures were computed
with some minimal filtering using Unix text utilities that work with files
based on their extension, for example, *.c and *.cpp to capture C and
C++ source files respectively. These approaches have the advantage of
providing a general trend quickly and are practical when attempting to
process many thousands of projects. The file based processing method,
however does not directly mine any structural dependency information.
It also includes source code files that may no longer be part of the code
base – essentially unused and unreachable code that has not been removed
from the repositories.
This practice of leaving old code has been noted by researchers in the
field of code clone detection who observed the tendency of developers
to copy a block of code, modify it, and leave the old code still in the
repository [5,135,155,157]. Godfrey et al. [100] in their study of Linux
kernel evolution noted that depending on the configuration setting in
the build script (Makefile), it is possible that only 15% of the Linux
source files are part of the final build. The use of only a small set of
source for a release is common in software that can be built for multiple
environments. For instance, Linux is an operating system designed to
run on a large range of hardware platforms. When building the operating
system for a specific hardware configuration, many modules are not
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