Abstract: To meet the needs of short response time as well as the reliability, cooperative applications usually adopt fully replicated architecture In such systems, many users manipulate the same object at different sites online or offline Usually these objects are called replicas and it is a great challenge to keep the consistency of these replicas and obtain a common state at last To solve this problem, various requirements of online and offline cooperation are analyzed first and then the corresponding control mechanisms, i e , a synchronization algorithm for online mode and an object merging algorithm for offline mode, are proposed based on the results The mechanisms have been implemented in a general cooperation support platform named Cova Real world practice shows that when applied with other mechanisms, the two algorithms can meet the data consistency needs of cooperative applications very well