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)
S. Doerfel, D. Zoller, P. Singer, T. Niebler, A. Hotho, and M. Strohmaier. Proceedings of the 16th LWA Workshops: KDML, IR and FGWM, Aachen, Germany, September 8-10, 2014., volume 1226 of CEUR Workshop Proceedings, page 18--19. CEUR-WS.org, (2014)