Extracting Prehistories of Software Refactorings from Version Archives

This paper proposes an automated technique to extract prehistories of software refactorings from existing software version archives, which in turn a technique to discover knowledge for finding refactoring opportunities. We focus on two types of knowledge to extract: characteristic modification histories, and fluctuations of the values of complexity measures. First, we extract modified fragments of code by calculating the difference of the Abstract Syntax Trees in the programs picked up from an existing software repository. We also extract past cases of refactorings, and then we create traces of program elements by associating modified fragments with cases of refactorings for finding the structures that frequently occur. Extracted traces help us identify how and where to refactor programs, and it leads to improve the program design.