Distributed groupware systems provide computer support for manipulating shared objects by dispersed users. Data replication is used in such systems in order to improve the availability of data. This potentially leads to divergent (or different) replicas. In this respect, the Operational Transformation (OT) approach is employed to maintain convergence of all replicas, all users view the same object. Using this approach, users can exchange their updates in any order since the convergence should be ensured in all cases. However, designing correct OT algorithms is still an open issue. In this paper, we demonstrate that recent OT algorithms are incorrect. We analyse the source of this problem and we propose a generic solution with its formal correctness.
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