ABSTRACT
Rough set theory is a kind of mathematical method driven by practical needs to deal with vagueness and uncertainty. e main idea of rough set theory is based on the indiscernibility relation that every object is associated with a certain amount of information and the object can only be expressed by means of some obtained information. erefore, objects with the same or similar information can be indiscernible with respect to the available information. e indiscernible blocks formed by indiscernible objects of the universe are called the element sets or the knowledge granularity. Based on the knowledge used in approximation, the universe is divided into some element sets of the indiscernible objects that are based on conditional attribute sets, and the element sets are regarded as approximate “knowledge granularity”; the knowledge used in approximation would divide the universe into the decision-making class derived from the decision attribute sets, on this basis, and one kind of knowledge can be used to approximate the other. When approximation is inaccurate, roughness would appear.
