Abstract：The classical rough set theory is not useful for analyzing incomplete information system, and this problem is solved by tolerance relation, similarity relation, limited tolerance relation and completed tolerance relation to some extent. Limitations of these models were analyzed, and on the basis of the completed tolerance relation an extended rough set model based on improved complete tolerance relation was developed. The extended model not only retains the merits of the existing models, but also overcomes the limitations of the existing models to some extent. The result of case studies shows the effectiveness of the presented model.
2010, Vol. 30 
