“…The DTRS approach approximates a given concept or a set by three regions (positive, negative and boundary regions) which correspond to positive, negative and boundary rules in threeway decisions (3WDs), respectively [11,50,51]. It has been applied to text classification [20,23], web-based support systems [54], cluster analysis [27,58], investment decisions [30], multi-classification [6,26,27], email filtering [17,63], government decisions [28], face recognition [22] etc. In the following, we first review developments of PRSs, DTRSs and 3WDs; then we present the main work of this paper.…”