R. Agrawal, J. Gehrke, D. Gunopulos, and P. Raghavan. Proceedings of the ACM SIGMOD Int'l Conference on Management of Data, Seattle, Washington, page 94--105. ACM Press, (June 1998)
M. Atzmueller, D. Benz, A. Hotho, and G. Stumme (Eds.) Technical report (KIS), 2010-10 Department of Electrical Engineering/Computer Science, Kassel University, (2010)