Background: Accurate representation of developer expertise has always been an important research problem. While a number of studies proposed novel methods of representing expertise within individual projects, these methods are difficult to apply at an ecosystem level. However, with the focus of software development shifting from monolithic to modular, a method of representing developers' expertise in the context of the entire OSS development becomes necessary when, for example, a project tries to find new maintainers and look for developers with relevant skills. Aim: We aim to address this knowledge gap by proposing and constructing the Skill Space where each API, developer, and project is represented and postulate how the topology of this space should reflect what developers know (and projects need). Method: we use the World of Code infrastructure to extract the complete set of APIs in the files changed by open source developers and, based on that data, employ Doc2Vec embeddings for vector representations of APIs, developers, and projects. We then evaluate if these embeddings reflect the postulated topology of the Skill Space by predicting what new APIs/projects developers use/join, and whether or not their pull requests get accepted. We also check how the developers' representations in the Skill Space align with their self-reported API expertise. Result: Our results suggest that the proposed embeddings in the Skill Space appear to satisfy the postulated topology and we hope that such representations may aid in the construction of signals that increase trust (and efficiency) of open source ecosystems at large and may aid investigations of other phenomena related to developer proficiency and learning.

The data collected from open source projects provide means to model large software ecosystems, but often suffer from data quality issues, specifically, multiple author identification strings in code commits might actually be associated with one developer. While many methods have been proposed for addressing this problem, they are either heuristics requiring manual tweaking, or require too much calculation time to do pairwise comparisons for 38M author IDs in, for example, the World of Code collection. In this paper, we propose a method that finds all author IDs belonging to a single developer in this entire dataset, and share the list of all author IDs that were found to have aliases. To do this, we first create blocks of potentially connected author IDs and then use a machine learning model to predict which of these potentially related IDs belong to the same developer. We processed around 38 million author IDs and found around 14.8 million IDs to have an alias, which belong to 5.4 million different developers, with the median number of aliases being 2 per developer. This dataset can be used to create more accurate models of developer behaviour at the entire OSS ecosystem level and can be used to provide a service to rapidly resolve new author IDs.

Evidence shows that developer reputation is extremely important when accepting pull requests or resolving reported issues. It is particularly salient in Free/Libre Open Source Software since the developers are distributed around the world, do not work for the same organization and, in most cases, never meet face to face. The existing solutions to expose developer reputation tend to be forge specific (GitHub), focus on activity instead of impact, do not leverage social or technical networks, and do not correct often misspelled developer identities. We aim to remedy this by amalgamating data from all public Git repositories, measuring the impact of developer work, expose developer's collaborators, and correct notoriously problematic developer identity data. We leverage World of Code (WoC), a collection of an almost complete (and continuously updated) set of Git repositories by first allowing developers to select which of the 34 million(M) Git commit author IDs belong to them and then generating their profiles by treating the selected collection of IDs as that single developer. As a side-effect, these selections serve as a training set for a supervised learning algorithm that merges multiple identity strings belonging to a single individual. As we evaluate the tool and the proposed impact measure, we expect to build on these findings to develop reputation badges that could be associated with pull requests and commits so developers could easier trust and prioritize them.