Ickjai Lee Kyungmi Lee Higher Order Voronoi Diagrams for Concept Boundaries and Tessellations. 513-518 2007 conf/ACISicis/2007 ACIS-ICIS http://doi.ieeecomputersociety.org/10.1109/ICIS.2007.106 db/conf/ACISicis/ACISicis2007.html#LeeL07