1. Van Steen M. R. and Sassen J. M. A. COGSYS-KRL: a knowledge representation language for real-time knowledge based systems. In Proceedings AI Toepassingen '89 (Edited by van den Herik H. J.), pp. 331–340. SIC, The Hague (in Dutch).
2. The knowledge level;Newell;AI Mag.,1981
3. Components of expertise;Steels;AI Mag.,1990
4. The engineering of XCON;Bachant;Commun, ACM,1989