“…Rough set theory 1,2,3,4 , proposed by Pawlak, has been demonstrated to be useful in pattern recognition, knowledge discovery 5,6 , decision support 7,8 , data mining, feature selection, medical diagnosis and so on. Pawlak's rough set, is constructed on the basis of an indiscernibility relation, which is an equivalence relation and then such model can be used to unravel decision rules from the information system with decision attributes, such system can also be referred to as decision system in many rough set literatures.…”