Keiichi Nakata Angi Voß Marcus Juhnke Thomas Kreifelts Collaborative Concept Extraction from Documents. 1998 conf/pakm/1998 PAKM http://SunSITE.Informatik.RWTH-Aachen.DE/Publications/CEUR-WS/Vol-13/paper20.ps db/conf/pakm/pakm1998.html#NakataVJK98