Wesley W. Chu Kuorong Chiang Chih-Cheng Hsu Henrick Yau An Error-based Conceptual Clustering Method for Providing Approximate Query Answers. 216-230 1996 39 Commun. ACM 12es db/journals/cacm/cacm39.html#ChuCHY96 CACMs1/CACM3912/P0216.pdf http://doi.acm.org/10.1145/272682.272714