• knowledge acquisition and engineering, which deals with the bottleneck of acquiring and modeling knowledge (the human-oriented problem), and
• knowledge representation, which deals with the bottleneck of representing knowledge and reasoning about it (the computer-oriented problem).
Dieter Fensel is an associate professor at the Division of Mathematics and Computer Science, Vrije Universiteit, Amsterdam, and a new department editor for Trends & Controversies. 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; firstname.lastname@example.org; www.cs.vu.nl/~dieter.
Mark A. Musen is an associate professor of medicine (medical informatics) and computer science at Stanford University and is head of the Stanford Medical Informatics laboratory. He conducts research related to knowledge acquisition for intelligent systems, knowledge-system architecture, and medical-sdecision support. He has directed the Protégé project since its inception in 1986, emphasizing the use of explicit ontologies and reusable problem-solving methods to build robust knowledge-based systems. He has an MD from Brown University and a PhD from Stanford. Contact him at Stanford Medical Informatics, 251 Campus Dr., Stanford Univ., Stanford, CA 94305; email@example.com; http://smi-web.stanford.edu/people/musen.