Stable Prediction of Defect-Inducing Software Changes (SPDISC)

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Context: software systems have become ever larger and more complex. This inevitably leads to software defects, whose debugging is estimated to cost the global economy 312 billion USD annually. Reducing the number of software defects is a challenging problem, and is particularly important considering the strong pressure towards rapid delivery. Such pressure impedes different parts of the software source code to all receive equally large amount of inspection and testing effort. With that in mind, machine learning approaches have been proposed for predicting defect-inducing changes in the source code as soon as these changes finish being implemented. Such approaches could enable software engineers to target special testing and inspection attention towards parts of the source code most likely to induce defects, reducing the risk of committing defective changes. Problem: the predictive performance of existing approaches is unstable, because the underlying defect generating process being modelled may vary over time (i.e., there may be concept drift). This means that practitioners cannot be confident about the prediction ability of existing approaches -- at any given point in time, predictive models may be performing very well or failing dramatically.Aim and vision: SPDISC aims at creating more stable models for predicting defect-inducing changes, through the development of a novel machine learning approach for automatically adapting to concept drift. When integrated with software versioning systems, the models will provide early, reliable and automated defect-inducing change alerts throughout the lifetime of software projects. Impact: SPDISC will enable a transformation in the way software developers review and commit their changes. By creating stable models to make software developers aware of defect-inducing changes as soon as these are implemented, it will allow targeted inspection and testing attention towards defect-inducing code throughout the lifetime of software projects. This will reduce the debugging cost and ultimately lead to better software quality. Proposed approach: an online learning algorithm will be developed to process incoming data as they become available, enabling fast reaction to concept drift. Concept drift will be detected using methods designed to cope with class imbalance, which typically occurs in prediction of defect-inducing software changes. Class imbalance refers to the issue of having a much smaller number of defect-inducing changes than the number of safe changes. The proposed approach will also make use of data from different projects (i.e., transfer learning between domains) to speed up adaptation to concept drift.Novelty: SPDISC is the first proposal to look into the stability of predictive performance over time in the context of defect-inducing software changes. Most previous work ignored the fact that predictions are required over time, being oblivious of the instability of predictive performance in this problem. To deal with instability, SPDISC will develop the first online transfer learning approach for predicting defect-inducing software changes. Ambitiousness: online transfer learning between domains with concept drift is not only a very new area of research in software engineering, but also in machine learning. Very few approaches exist for that, and none of them can deal with class-imbalanced problems. Therefore, SPDISC will not only advance software engineering by enabling a transformation in the way software developers review and commit their changes, but also advance the area of machine learning itself. Timeliness: given the current size and complexity of software systems, the increased number of life-critical applications, and the high competitiveness of the software industry, approaches for improving software quality and reducing the cost of producing and maintaining software are currently of utmost importance.