thesis - Faculty of Information and Communication Technologies ...

Chapter 1. Introduction
1.2 Research Approach
Empirical research by its very nature relies heavily on quantitative information.
Our research is based on an exploratory study of forty nontrivial
and popular Java Open Source Software Systems and the results
and interpretation are from an empirical software engineering perspective.
The data set consists of over 1000 distinct releases encompassing
an evolution history comprising approximately 55000 classes. We investigate
Open Source Software Systems due to their non-restrictive
licensing, ease of access, and their growing use in a wide range of
projects.
Our approach involves collecting metric data by processing compiled
binaries (Java class files) and analysing how these metrics change over
time in order to understand both growth as well as change. Although we
use the compiled builds as input for our analysis, we also make use of
other artifacts such as revision logs, project documentation, and defect
logs as well as the source code in order to interpret our findings and
better understand any abnormal change events. For instance, if the size
of the code base has doubled between two consecutive releases within
a short time frame (as observable in the history), additional project
documentation and messages on the discussion board often provide an
insight into the rationale and motivations within the team that cannot
be directly ascertained from an analysis of the binaries alone.
In order to understand the nature of growth, we construct relative and
absolute frequency histograms of the various metrics and then observe
how these histograms change over time using higher-order statistical
techniques. This method of analysis allows us, for example, to identify
if a certain set of classes is gaining complexity and volume at the
expense of other classes in the software system. By analysing how developers
choose to distribute functionality, we can also identify if there
are common patterns across software systems and if evolutionary pressures
have any impact on how developers organise software systems.
We examine the nature of change, by analyzing software at two levels of
granularity: version level and class level. The change measures that we
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