Even though there has been some research on system evolution, there is no well defined vocabulary to indicate deviation of a system from desired goals. Further, there are no objective measures to indicate whether changes incorporated into a system as part of its evolution violates the integrity of the architectural design. Also, little research has been done to categorize the aspects of a software system that is subject to deviation as the system evolves.

In this paper we develop a model for tracking software evolution and propose measures that will objectively indicate the extent of deviation or divergence in a software system. We also categorize the different aspects of software, changes to which can significantly impact usability as well as conceptual coherence.