1. Pawlak, Z.: Classification of objects by means of attributes. Pol. Acad. Sci. 429 (1981)
2. Pawlak, Z.: Rough sets. Int. J. Comput. Inf. Sci. 11, 341–356 (1982)
3. Pawlak, Z.: Information Systems. Theoretical Foundations. WNT, Warsaw (1983) (in Polish)
4. Pawlak, Z.: Rough Sets. Theoretical Aspects of Reasoning About Data. Kluwer Academic, Dordrecht (1991)
5. Pawlak, Z., Skowron, A.: Rudiments of rough sets. Inf. Sci. 177, 3–27 (2007)