variED: An Editor for Collaborative, Real-Time Feature Modeling.

This work was published in Empirical Software Engineering (EMSE) 26, 2 (2021) [Ku21]. Feature models are a helpful means to document, manage, maintain, and configure the variability of a software system. Various stakeholders in an organization may get involved in modeling the features in such a software system. Currently, collaboration in such a scenario can only be done with face-to-face meetings or by combining single-user feature-model editors with additional communication and version-control systems. While face-to-face meetings are often costly and impractical, using version-control systems can cause merge conflicts and inconsistency within a model. Advanced tools that solve these problems by enabling collaborative, real-time feature modeling, analogous to Google Docs or Overleaf for text editing, are missing. We describe the formal foundations of collaborative, real-time feature modeling; a conflict resolution algorithm; proofs that our formalization converges and preserves causality as well as user intentions; a prototype; and the results of an empirical evaluation to assess the prototype's usability. Our contributions provide the basis for advancing existing feature-modeling practices to support collaborative feature modeling. Our prototype is considered helpful and valuable by 17 users, also indicating opportunities for new research directions.