Incrementally updating approximation in incomplete iformation systems under the variation of objects

Abstract

In covering approximation space, the rough membership functions give numerical charac terizations of covering-based rough set approximations. It is considered as a tool for establishing the relationship between covering-based rough sets and fuzzy covering-based rough sets. In this paper, we introduce a new method to update the approximation sets with rough membership functions in covering approximation space. Firstly, we present the third types of rough membership functions and study their properties. And then, we consider the change of them while simultaneously adding and removing objects in the information system. Based on that change, we propose a method for upda ting the approximation sets when the objects vary over time. We proved that the method facilitates knowledge maintenance without retrain from scratch.