The subject invention pertains to data synchronization across replicas. Disclosed are systems and methods of detecting and handling constraint-based conflicts that occur during a synchronization session. In accordance with one particular aspect of the invention, name-constraint violations can be detected. These violations can be resolved by generating a single merged identity that can be utilized to refer to data units, for example on different replicas that had the same name. A property of the merged identity can be merge history, which specifies the identifiers subsumed by the merge.