Real Differences between OT and CRDT under a General Transformation Framework for Consistency Maintenance in Co-Editors.

OT (Operational Transformation) was invented for supporting real-time co-editors in the late 1980s and has evolved to become a core technique used in today's working co-editors and adopted in major industrial products. CRDT (Commutative Replicated Data Type) for co-editors was first proposed around 2006, under the name of WOOT (WithOut Operational Transformation). Follow-up CRDT variations are commonly labeled as "post-OT" techniques and have made broad claims of superiority over OT, in terms of correctness, time and space complexity, etc. Over one decade later, however, OT remains the choice for building the vast majority of co-editors, whereas CRDT is rarely found in working co-editors. Contradictions between the reality and CRDT's purported advantages have been the source of much confusion and debate in co-editing communities. What is CRDT really to co-editing? What are the real differences between OT and CRDT for co-editors? What are the key factors that may have affected the adoption of and choice between OT and CRDT for co-editors in the real world? A thorough examination of these questions is relevant not only to researchers exploring the frontiers of co-editing technologies, but also to practitioners seeking viable techniques to build real world applications. Based on comprehensive reviews on representative OT and CRDT solutions and working co-editors based on them, we present our discoveries, in relation to these questions and beyond, in three articles. We also reveal facts and present evidences that refute CRDT claimed advantages over OT. We hope the discoveries from this work help clear up common misconceptions and confusions surrounding OT and CRDT, and accelerate progress in co-editing technology for real world applications.