Salvatore Greco Benedetto Matarazzo Roman Slowinski Dominance-Based Rough Set Approach and Bipolar Abstract Rough Approximation Spaces. 31-40 2008 RSCTC http://dx.doi.org/10.1007/978-3-540-88425-5_4 conf/rsctc/2008 db/conf/rsctc/rsctc2008.html#GrecoMS08