KI-97: Advances in Artificial Intelligence 21st Annual German Conference on Artificial Intelligence, Freiburg, Germany, September 9-12, 1997, Proceedings - Brewka, Gerhard; Brewka, Gerhard; Habel, Christopher; Habel, Christopher; Nebel, Bernhard; Nebel, Bernhard (Springer Berlin Heidelberg : Imprint: Springer, 1997)