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 solutions, in terms of correctness, time and space complexity, simplicity, etc . Over one decade later, however,  OT remains the choice for building the vast majority of  co-editors , whereas CRDTis rarely found in working co-editors. Why? Based on comprehensive review and comparison on representative OT and CRDT solutions and co-editors based on them , we present our discoveries in relation to this question and beyond in a series of three articles. In prior work, we have revealed that CRDT is like OT in following the same general transformation approach and CRDT is not natively commutative for concurrent operations in co-editors, which helps to clarify what CRDT really is and is not for co-editors. In this article , we reveal OT and CRDT differences in correctness and complexity by dissecting and examining representative OT and CRDT solutions. We explore how different basic approaches , i.e. the concurrency-centric approach taken by OT and the content-centric approach taken by CRDT, had resulted in different technical challenges , correctness and complexity issues , and solutions . Moreover, we reveal hidden  algorithmic flaws with representative CRDT solutions, and discuss common myths and facts related to correctness , time and space complexity , and simplicity of OT and CRDT . We present facts and evidences that refute CRDT claimed advantages over OT .
OT (Operational Transformation) was invented for supporting real-time co-editors in the late 1980s and has evolved to become core techniques widely used in today's working co-editors and adopted in 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 capable of making concurrent operations natively commutative in co-editors. On top of that, CRDT solutions have made broad claims of superiority over OT solutions, and often portrayed OT as an incorrect and inefficient technique . Over one decade later, however, CRDT is rarely found in working co-editors; OT remains the choice for building the vast majority of today's co-editors . Contradictions between the reality and CRDT's purported advantages have been the source of much confusion and debate among co-editing researcher sand developers. To seek truth from facts, we set out to conduct a comprehensive and critical review on representative OT and CRDT solutions and co-editors based on them . From this work, we have made important discoveries about OT and CRDT, and revealed facts and evidences that refute CRDT claims over OT on all accounts. These discoveries help explain the underlying reasons for the choice between OT and CRDT in the real world. We report these results in a series of three articles. In the second article of this series , we reveal the differences between OT and CRDT in their basic approaches to realizing the same general transformation and how such differences had resulted in different challenges and consequential correctness and complexity issues . Moreover, we reveal hidden complexity and algorithmic flaws with representative CRDT solutions, and discuss common myths and facts related to correctness and complexity of OT and CRDT .
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capable of making concurrent operations natively commutative in co-editors. On top of that, CRDT solutions
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in terms of correctness, time and space complexity, simplicity, etc
and often portrayed OT as an incorrect and inefficient technique
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CRDT is rarely found in working co-editors;
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today's
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, whereas CRDTis rarely found in working co-editors. Why? Based on comprehensive review and comparison
. Contradictions between the reality and CRDT's purported advantages have been the source of much confusion and debate among co-editing researcher sand developers. To seek truth from facts, we set out to conduct a comprehensive and critical review
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, we present our discoveries in relation to this question and beyond in a series of three articles. In prior
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revealed that CRDT is like OT in following the same general transformation approach and CRDT is not natively commutative for concurrent operations in co-editors, which helps to clarify what CRDT really is and is not for co-editors. In this article
made important discoveries about OT and CRDT, and revealed facts and evidences that refute CRDT claims over OT on all accounts. These discoveries help explain the underlying reasons for the choice between OT and CRDT in the real world. We report these results in a series of three articles. In the second article of this series
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OT and CRDT differences in correctness and complexity by dissecting and examining representative
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solutions. We explore how different basic approaches , i.e. the concurrency-centric approach taken by OT and the content-centric approach taken by CRDT,
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technical challenges ,
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, and solutions
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, time and space complexity , and simplicity
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. We present facts and evidences that refute CRDT claimed advantages over OT