Abstract: The set valued information system is an extension of the general model of the information system. In real-life applications,the information system changes dynamically according to the variation of objects. I}his paper discussed the changing rules of approximations under the tolerance relation when objects vary with time and presents properties of the variation of approximations in set valued information systems and set valued decision information systems. Examples are given to illustrate the validity of the proposed properties.

Key words: Rough sets, Set-valued information system, Incrcmcntal updating, Tolerance relation