thesis - Faculty of Information and Communication Technologies ...

Chapter 2. Software Evolution
Process of Biological Evolution
Directed Selection
(based on fitness)
Population
Random Variation
(Reproduction)
Process of Software Evolution
Directed Adaptation
(based on feedback/external pressures)
Software System
Figure 2.1: The process of evolution.
al. [82] studied how database management systems evolve. The term
in relation to how a software system changes started to appear in work
done by Couch [57]. Building on this foundation, Lehman [174], in his
seminal work argued that E-type software (application software used
in the real-world) due to their very use provide evolutionary pressures
that drive change. This argument was supported by the observation
that stakeholder requirements continually change, and in order to stay
useful, a software system must be adapted to ensure ongoing satisfaction
of the stakeholders. Unlike biological evolution which applies to a
population of organisms, the term software evolution is used within the
context of an individual software system. Similar to biological evolution,
the process of evolution in software is directed and feedback-driven to
ensure the software system is continuously adapted to satisfy the user’s
requirements. However, a key distinction is that in software evolution,
there is no random variation occurring within the software system (see
Figure 2.1) and the term “evolution” in the context of software implies
directed adaptation.
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