Operational Transformation (OT) is a technology to provide consistency maintenance and concurrency control in real-time collaborative editing systems. The correctness of OT is critical due to its foundation role in supporting a wide range of real world applications. In this work, we formally model the OT-based collaborative editing systems and establish their correctness, w.r.t. convergence and intention preservation, using a set of well-defined transformation conditions and properties. We then use model checking to verify the transformation properties for basic data and operational models. To the best of our knowledge, this is the first work to conduct a complete verification of OT including control algorithms and transformation functions. Our evaluation confirmed the correctness of existing OT systems and transformation functions with important discoveries.
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