Clone detection and clone manipulation

The DRY principle says that a particular code fragment should not be repeated more than once in a program. But it happens. And when it does, it is good to be able to find the multiple code "clones" because Software cloning complicates the maintenance process by giving the maintainers unnecessary code to examine. As per Burd, it seems that when presented with the challenge of adding new functionality the natural instinct of a programmer is to copy, paste and modify the existing code to meet the new requirements and thus creating a software clone. While the basis behind such an approach is uncertain, one possible reason is due to time restrictions on maintainers to complete the maintenance change. Duccase points out that “making a code fragment is simpler and faster than writing from scratch” and that if a programmer’s pay is related to the amount of code they produce then the proliferation of software clones will continue.

Once a clone is created it is effectively lost within the source code and so both clones must therefore be maintained as separate units despite their similarities. Komondoor states that if errors are identified within one clone then it is likely that modifications may be necessary to the other counter-part clones. Detection is therefore required if any of the clones are to be re-identified to assist the maintenance process. So if clones can be detected then the similarities can be exploited and replaced during preventative maintenance with a new single code unit this will eliminate the problems identified above.

There are a good number of clone detection tools available both commercially and within academia. Within these tools several different approaches to software clone detection have been implemented, including string analysis, program slicing, metric analysis and abstract tree comparisons. This page will survey the a set of clone detection tools and compare them.