Abstract: An incomplete information system is a generalization of an information system, which has wide applications in many domains. The approximations of concepts may vary when the information system is dynamically changing. It is meaningful to study how to update the approximations by using the original information. `hhe dynamic changes of information systems can be considered in the three aspects:the coarsening and refining of attribute valucs,the attribute set and the object set, This paper only focused on the approaches for updating approximations when coarsening and refining attribute values. The definitions of attribute values coarsening and refining in the incomplete information system were given. I}hen approaches for updating the approximations were discussed when coarsening and refining attribute values under the characteristic relation. Finally, several examples were given to illustrate the validity of the proposed approaches.

Key words: Rough set, Granular computing, Incomplete information system, Characteristic relation, Incremental updating