Many open source projects provide good first issues (GFIs) to attract and retain newcomers. Although several automated GFI recommenders have been proposed, existing recommenders are limited to recommending generic GFIs without considering differences between individual newcomers. However, we observe mismatches between generic GFIs and the diverse background of newcomers, resulting in failed attempts, discouraged onboarding, and delayed issue resolution. To address this problem, we assume that personalized first issues (PFIs) for newcomers could help reduce the mismatches. To justify the assumption, we empirically analyze 37 newcomers and their first issues resolved across multiple projects. We find that the first issues resolved by the same newcomer share similarities in task type, programming language, and project domain. These findings underscore the need for a PFI recommender to improve over state-of-the-art approaches. For that purpose, we identify features that influence newcomers' personalized selection of first issues by analyzing the relationship between possible features of the newcomers and the characteristics of the newcomers' chosen first issues. We find that the expertise preference, OSS experience, activeness, and sentiment of newcomers drive their personalized choice of the first issues. Based on these findings, we propose a Personalized First Issue Recommender (PFIRec), which employs LamdaMART to rank candidate issues for a given newcomer by leveraging the identified influential features. We evaluate PFIRec using a dataset of 68,858 issues from 100 GitHub projects. The evaluation results show that PFIRec outperforms existing first issue recommenders, potentially doubling the probability that the top recommended issue is suitable for a specific newcomer and reducing one-third of a newcomer's unsuccessful attempts to identify suitable first issues, in the median. We provide a replication package at https://zenodo.org/record/7915841.

Although the open source model bears many advantages in software development, open source projects are always hard to sustain. Previous research on open source sustainability mainly focuses on projects that have already reached a certain level of maturity (e.g., with communities, releases, and downstream projects). However, limited attention is paid to the development of (sustainable) open source projects in their infancy, and we believe an understanding of early sustainability determinants is crucial for project initiators, incubators, newcomers, and users.

Attracting and retaining newcomers is vital for the sustainability of an open-source software project. However, it is difficult for newcomers to locate suitable development tasks, while existing "Good First Issues" (GFI) in GitHub are often insufficient and inappropriate. In this paper, we propose RecGFI, an effective practical approach for the recommendation of good first issues to newcomers, which can be used to relieve maintainers' burden and help newcomers onboard. RecGFI models an issue with features from multiple dimensions (content, background, and dynamics) and uses an XGBoost classifier to generate its probability of being a GFI. To evaluate RecGFI, we collect 53,510 resolved issues among 100 GitHub projects and carefully restore their historical states to build ground truth datasets. Our evaluation shows that RecGFI can achieve up to 0.853 AUC in the ground truth dataset and outperforms alternative models. Our interpretable analysis of the trained model further reveals interesting observations about GFI characteristics. Finally, we report latest issues (without GFI-signaling labels but recommended as GFI by our approach) to project maintainers among which 16 are confirmed as real GFIs and five have been resolved by a newcomer.

Release notes (RNs) summarize main changes between two consecutive software versions and serve as a central source of information when users upgrade software. While producing high quality RNs can be hard and poses a variety of challenges to developers, a comprehensive empirical understanding of these challenges is still lacking. In this paper, we bridge this knowledge gap by manually analyzing 1,731 latest GitHub issues to build a comprehensive taxonomy of RN issues with four dimensions: Content, Presentation, Accessibility, and Production. Among these issues, nearly half (48.47%) of them focus on Production; Content, Accessibility, and Presentation take 25.61%, 17.65%, and 8.27%, respectively. We find that: 1) RN producers are more likely to miss information than to include incorrect information, especially for breaking changes; 2) improper layout may bury important information and confuse users; 3) many users find RNs inaccessible due to link deterioration, lack of notification, and obfuscate RN locations; 4) automating and regulating RN production remains challenging despite the great needs of RN producers. Our taxonomy not only pictures a roadmap to improve RN production in practice but also reveals interesting future research directions for automating RN production.

To facilitate newcomer onboarding, GitHub recommends the use of "good first issue" (GFI) labels to signal issues suitable for newcomers to resolve. However, previous research shows that manually labeled GFIs are scarce and inappropriate, showing a need for automated recommendations. In this paper, we present GFI-Bot (accessible at https://gfibot.io), a proof-of-concept machine learning powered bot for automated GFI recommendation in practice. Project maintainers can configure GFI-Bot to discover and label possible GFIs so that newcomers can easily locate issues for making their first contributions. GFI-Bot also provides a high-quality, up-to-date dataset for advancing GFI recommendation research.

The safe operation of physical systems typically relies on high-quality models. Since a continuous stream of data is generated during run-time, such models are often obtained through the application of Gaussian process regression because it provides guarantees on the prediction error. Due to its high computational complexity, Gaussian process regression must be used offline on batches of data, which prevents applications, where a fast adaptation through online learning is necessary to ensure safety. In order to overcome this issue, we propose the LoG-GP. It achieves a logarithmic update and prediction complexity in the number of training points through the aggregation of locally active Gaussian process models. Under weak assumptions on the aggregation scheme, it inherits safety guarantees from exact Gaussian process regression. These theoretical advantages are exemplarily exploited in the design of a safe and data-efficient, online-learning control policy. The efficiency and performance of the proposed real-time learning approach is demonstrated in a comparison to state-of-the-art methods.