Using Conflict-free Replicated Data Types to support Block Editing

Abstract

Recent times once more informed us on the relevance of capable online collaborative tools. For our online collaborative XML editor, we have looked into technologies for constrained block editing which, obeying schemas such as with XML, permit on-and off-line users or agents to add, delete, copy, move, split and merge blocks of text. To that end, we studied the current state of Operational Transformations (OT) and Conflict-free Replicated Data Types (CRDT). Furthermore, after selection of the best-ranking enabling technology, we studied existing CRDT implementations for unstructured texts, and extended a Logootbased CRDT to implement on-and offline split and merge block support. We designed a generic concept and created a scientific prototype to test the concept on its correctness. For now, we neglected undo and redo operations. Within these limitations, we show that our prototype converges under most circumstances. We verify causality and assess the experience of user editing intent. Finally, we give an outlook and design recommendations for production implementations, and suggestions for tackling the problem of cyclic references in block mergers.