1. Budd, T.A.: An introduction of object-oriented programming, 2nd edn. Addison Wesley Longman, Reading (1997)
2. Kryszkiewicz, M.: Rough set approach to incomplete information systems. Information science 112, 39–49 (1998)
3. Kudo, Y., Murai, T.: A theoretical formulation of object-oriented rough set models. Journal of advanced computational intelligence and intelligent informatics 10(5), 612–620 (2006)
4. Kudo, Y., Murai, T.: A note on treatment of incomplete information in object–oriented rough sets. In: Proc. of the joint 3rd international conference on soft computing and intelligent systems and 7th international symposium on advanced intelligent systems, pp. 2238–2243 (2006)
5. Lecture Notes in Artificial Intelligence;Y.. Kudo,2006