Provided are a data management method, device and system for synchronizing data without prior knowledge of the data's structure. When any application is activated, application data is created and also an application data change log is created to indicate a change in the application data. In addition, a schema table defining a data structure for storing the application data is created and also a schema table change log indicating a change in the schema table is created. Based on such data and logs, a client and a server can share data without a prior agreement in data schema.