Incremental approaches for updating approximations in set-valued ordered information systems

Incremental learning is an efficient technique for knowledge discovery in a dynamic database, which enables acquiring additional knowledge from new data without forgetting prior knowledge. Rough set theory has been successfully used in information systems for classification analysis. Set-valued information systems are generalized models of single-valued information systems, which can be classified into two categories: disjunctive and conjunctive. Approximations are fundamental concepts of rough set theory, which need to be updated incrementally while the object set varies over time in the set-valued information systems. In this paper, we analyze the updating mechanisms for computing approximations with the variation of the object set. Two incremental algorithms for updating the approximations in disjunctive/conjunctive set-valued information systems are proposed, respectively. Furthermore, extensive experiments are carried out on several data sets to verify the performance of the proposed algorithms. The results indicate the incremental approaches significantly outperform non-incremental approaches with a dramatic reduction in the computational speed.