After studying mathematics, sociology, and computer science in Berlin, he joined the Institute AIFB at the University of Karlsruhe. His major subject was knowledge engineering, and his PhD thesis was on a formal specification language for knowledge-based systems. Currently, his focus is on using ontologies to mediate access to heterogeneous knowledge sources and to apply them in knowledge management and e-commerce. Contact him at the Division of Mathematics and Computer Science, Vrije Universiteit Amsterdam, De Boelelaan 1081a, 1081 HV Amsterdam, Netherlands; dieter@cs.vu.nl; www.cs.vu.nl/~dieter.