J. Parker, A. Khoogar, and D. Goldberg. Robotics and Automation, 1989. Proceedings., 1989 IEEE International Conference on, page 271--276. IEEE, (1989)
R. Agrawal, T. Imielinski, and A. Swami. Proceedings of the 1993 ACM SIGMOD international conference on Management of Data (SIGMOD'93), page 207--216. ACM Press, (May 1993)
V. Vinge. Vision-21: Interdisciplinary Science and Engineering in the Era of Cyberspace, volume 10129 of NASA Conference Publication, page 11--22. Cleveland, OH, NASA Lewis Research Center, (1993)
E. Stopp, K. Gapp, G. Herzog, T. Laengle, and T. Lueth. KI-94: Advances in Artificial Intelligence, 18th German Annual Conference on Artificial Intelligence, Saarbrücken, volume 861 of Lecture Notes in Artificial Intelligence, Springer, Berlin, (1994)