Understanding the Evolution of Type-3 Clones: An Exploratory Study

Understanding the evolution of clones is important for both understanding the maintenance implications of clones and for building a robust clone management system. To this end, researchers have already conducted a number of studies to analyze the evolution of clones, mostly focusing on Type-1 and Type-2 clones. However, although there are a significant number of Type-3 clones in software systems, we know a little how they actually evolve. In this paper, we perform an exploratory study on the evolution of Type-1, Type-2, and Type-3 clones in six open source software systems written in two different programming languages and compare the result with a previous study to better understand the evolution of Type-3 clones. Our results show that although Type-3 clones are more likely to change inconsistently, the absolute number of consistently changed Type-3 clone classes is greater than that of Type-1 and Type-2. Type-3 clone classes also have a lifespan similar to that of Type-1 and Type-2 clones. In addition, a considerable number of Type-1 and Type-2 clones convert into Type-3 clones during evolution. Therefore, it is important to manage type-3 clones properly to limit their negative impact. However, various automated clone management techniques such as notifying developers about clone changes or linked editing should be chosen carefully due to the inconsistent nature of Type-3 clones.