Software evolution: the lifetime of fine-grained elements

Diomidis Spinellis; Panos Louridas; Maria Kechagia

doi:10.7717/peerj-cs.372

Software evolution: the lifetime of fine-grained elements

PeerJ Comput Sci. 2021 Feb 9:7:e372. doi: 10.7717/peerj-cs.372. eCollection 2021.

Authors

Diomidis Spinellis^{1

2}, Panos Louridas¹, Maria Kechagia³

Affiliations

¹ Department of Management Science and Technology, Athens University of Economics and Business, Athens, Greece.
² Department of Software Technology, Delft University of Technology, Delft, The Netherlands.
³ Department of Computer Science, University College London, London, UK.

Abstract

A model regarding the lifetime of individual source code lines or tokens can estimate maintenance effort, guide preventive maintenance, and, more broadly, identify factors that can improve the efficiency of software development. We present methods and tools that allow tracking of each line's or token's birth and death. Through them, we analyze 3.3 billion source code element lifetime events in 89 revision control repositories. Statistical analysis shows that code lines are durable, with a median lifespan of about 2.4 years, and that young lines are more likely to be modified or deleted, following a Weibull distribution with the associated hazard rate decreasing over time. This behavior appears to be independent from specific characteristics of lines or tokens, as we could not determine factors that influence significantly their longevity across projects. The programing language, and developer tenure and experience were not found to be significantly correlated with line or token longevity, while project size and project age showed only a slight correlation.

Keywords: Code decay; Hazard rate; Repository mining; Software aging; Software evolution.

Grants and funding

The project associated with this work has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 825328. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.