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Chapter 3. Data Selection Methodology
The selection criteria that each project must satisfy are as follows:
1. The system must be developed for the Java virtual machine. Source
code and compiled binaries are available for each release.
2. The software is a single coherent system, that is, it is a distribution
of a collection of related components packaged together.
3. At least 15 releases of the system are available. Only complete
releases with a version identifier are considered. Branches and
releases not derived from the main system tree are ignored. Minor
and major versions are both considered (for instance, Version
2.0, 2.1 and 3.0 are all considered. In this case, the version with
identifier 2.1 is often a release that provides minor enhancements
and/or defect corrections).
4. The system has been in actively development and use for at least
36 months.
5. The system comprises of at least 100 types (i.e., classes and interfaces)
in all releases under study.
6. Change logs do exist. This data provides the additional information
to understand the rationale behind the changes.
Further to the criteria for individual projects, we set a target of collecting
a minimum of 30 different software projects in order to ensure
we have sufficient diversity in our data set allowing some flexibility in
generalising our conclusions.
Rationale of Selection Criteria
Java is currently a popular language with wide spread use in both open
source and commercial projects. This popularity and usage has resulted
in a large amount of software developed using the Java programming
language. Despite its popularity and use in a variety of domains,
there are only a few studies that exclusively study release histories of
Java software systems [21, 193, 208, 270, 319]. Further, these studies
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