Description: In this paper, an information system with the indiscernibility relation has been considered. In the framework of this system the concepts of a rough set and its upper and lower approximations have been analyzed. The authors have considered a classical topological approach suggested by Z. Pawlak and a new algebraic method for data representation and processing based on the description of objects and their properties with the help of a system of unary predicates. Because of using such a method approximations of a rough set can be represented in the form of finite predicates algebra formulae.
Keywords: Rough sets theory, Rough Sets, upper approximation, lower approximation, indiscernibility relation, information system