Fourth International Workshop on Variability and Evolution of Software-Intensive Systems (VariVolution 2021)

Most of today's software systems evolve continuously and need to exist in various variants to address different requirements. However, changes resulting from evolution in time (i.e., revisions) and changes resulting from evolution in space (i.e., variants) are managed completely differently. In particular, no traditional technology for version management provides convenient means to effectively and efficiently support unified revision and variant management. Researchers from various communities have proposed new concepts and techniques to tackle this problem. Especially the communities of software configuration management, software product lines, and software versioning are working on such a unified technology. For example, variation control systems have been proposed to systematically manage revisions and variants based on a unified perspective of evolution in time and space. VariVolution (the 2nd International Workshop on Variability and Evolution of Software-Intensive Systems) aims to gather researchers and practitioners that are working on or interested in software evolution and variability. The workshop offers an opportunity to exchange ideas, report real-world cases and problems, and initiate new research directions and collaborations.