thesis - Faculty of Information and Communication Technologies ...

Chapter 2. Software Evolution
during the development of a specific release [25]. This is the analysis
technique preferred by change based studies (as discussed in Section
2.2). Though this approach is widely used in the literature [138],
there are significant limitations to this method of detecting change. The
transaction logs that are used as input for detecting change do not directly
record the nature of change. Specifically, they do not record if the
modification altered the functional semantics of the program, or if the
change was purely cosmetic [80]. For instance, widely used source code
control systems such as CVS and SVN record changes by string comparison
between two text files and tend to identify the lines added, removed
and modified. However, these tools do not check if the change impacts
the actual semantics of the program. That is, these tools treat the
following change actions identically – comment addition, source code
reformatting, and removing a method from a class. This inability of the
current generation of popular tools of recording the type of change is a
significant limitation if a study purely relies on data generated by these
tools to detect change. The limitation arises because changes to the
functional aspects of a class have a greater impact in maintenance as
they have the potential to impact other classes [281], and as a consequence
have a higher risk profile.
The second approach to detecting change analyses the actual class (or a
program file) at two different points in time in order to determine if it has
changed. This approach, referred to as origin analysis in the literature
[102,282] is comparatively more complex, but provides a more accurate
reflection of the changes since there is no reliance on reconstructing
change information by analysing an external transaction log. Detecting
change between two releases of a class has been an area of study for
many years [242,282] and different methods to assist in the detection of
the change have been developed [5,22,72,80,135,143,155,243,294]. In
this thesis, we detect changes by analysing classes in two consecutive
releases as it enables us to focus on changes to the functional aspects
of a program. A more detailed discussion of these techniques, their
strengths and limitations, as well as our own method for detecting the
change is presented in Chapter 6.
32