Besides contributing to clarify concepts and terminologies in the software engineering community, our work could also be used as a foundation for software evolution. For instance, on the basis of our analysis, a refined terminology for different kinds of software change may be proposed: Refactoring refers to the creation of new codes, keeping the identity of the program; re-engineering refers to the creation of new programs, keeping the identity of the software system; software evolution refers to the creation of new software systems, keeping the identity of the software product.