Extent, Extremum, and Curvature: Qualitative Numeric Features for Efficient Shape Retrieval. - Carbonell, Jaime G.; Siekmann, Jörg; Hertzberg, Joachim; Beetz, Michael; Englert, Roman; Gottfried, B.; Schuldt, A.; Herzog, O. (KI 2007: Advances in Artificial Intelligence, 2007)