Versioning Version Trees: The Provenance of Actions that Affect Multiple Versions

Change-based provenance captures how an entity is constructed; it can be used not only as a record of the steps taken but also as a guide during the development of derivative or new analyses. This provenance is captured as a version tree which stores a set of related entities and the exact changes made in deriving one from another. Version trees are generally viewed as monotonic---new nodes may be added but none are modified or deleted. However, there are a number of operations e.g., upgrades where this constraint leads to inefficient and unintuitive new versions. To address this, we propose a version tree without monotonicity where nodes may be modified and new actions inserted. We also propose to track the provenance of these tree changes to ensure that past version trees are not lost. This provenance is change-based; it links versions of version trees by the actions which transform the trees. Thus, we continue to track every change that impacts the evolution of an entity, but the actions are split between direct edits and changes to the version tree that affect multiple entity definitions. We show how this provenance leads to more intuitive and efficient operations on workflows and how this hybrid provenance may be understood.