This book consists of five chapters: Chapter one: It presented basic concepts of rough sets. Chapter two: In this chapter we used general relation to get a new class of near open sets which is called simply open set. Then we used this class to define a new approximation space as a generalization for the approximation space of Pawlak.In Chapter three we succeeded to introduce some properties of simply approximation space and give some counter examples to illustrate this relation with diagrams.In Chapter four: We define new rough membership relations, namely lower belong and upper belong.In Chapter five: we discuss new method to generate M S -approximation space based on the topology by using information system, we define the degree of dependency between them condition attributes and the decision attribute. Also we show the relation between them. We indicate new method of reduction based on simply open sets of the class of simply open sets.