B. Ganter, and C. Meschke. Rough Sets, Fuzzy Sets, Data Mining and Granular Computing, 12th International Conference, RSFDGrC 2009, Delhi, India, December 15-18, 2009. Proceedings, volume 5908 of Lecture Notes in Computer Science, page 117-126. (2009)
Y. Yao, and J. Mi. RSKT '09: Proceedings of the 4th International Conference on Rough Sets and Knowledge Technology, page 601--609. Berlin, Heidelberg, Springer-Verlag, (2009)