Stratified Rough Sets and Granular Computing

  title={Stratified Rough Sets and Granular Computing},
  author={Y. Y. Yao},
This paper examines granulation structures for stratified rough set approximations. With respect to different level of granulations, various approximations are obtained. Two special types of granulation structures are investigated. A nested sequence of granulations by equivalence relations leads to a nested sequence of rough set approximations. A hierarchical granulation, characterized by a special class of equivalence relations, leads to a more general approximation structure.