Change, Similarity and Redundancy in Software

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Software clones are defined to be duplicated or similar fragments of code in a software system. Copying a code fragment and reusing it by pasting with editing changes is a common practice in software development. Developers in fact often intentionally practice cloning because of the underlying benefits such as faster development, reuse of well-tested code by avoiding risks, or time limits assigned to them. On the other hand, clones are the #1 code “bad smell” in Flower’s refactoring list. Recent studies both with industrial and open source software show that while clones are not always harmful and clones can be useful in many ways, many of them can also be detrimental to software maintenance. Of course, reusing a fragment containing unknown bugs may result in fault propagation, or any changes in a cloned fragment may lead to changes to all the similar fragments to it, which is challenging, time consuming, and error-prone. Clones are thus considered to be one of the primary contributors to the high maintenance cost of software, which is up to 80% of the total development cost.