Validating the use of topic models for software evolution

Topics are collections of words that co-occur fre-quently in a text corpus. Topics have been found to be effective tools for describing the major themes spanning a corpus. Using such topics to describe the evolution of a software system’s source code promises to be extremely useful for development tasks such as maintenance and re-engineering. However, no one has yet examined whether these automatically discovered topics accurately describe the evolution of source code, and thus it is not clear whether topic models are a suitable tool for this task. In this paper, we take a first step towards deter-mining the suitability of topic models in the analysis of software evolution by performing a qualitative case study on 12 releases of JHotDraw, a well studied and documented system. We define and compute various metrics on the identified topics and manually investi-gate how the metrics evolve over time. We find that topic evolutions are characterizable through spikes and drops in their metric values, and that the large majority of these spikes and drops are indeed caused by actual change activity in the source code. We are thus encouraged by the use of topic models as a tool for analyzing the evolution of software. 1