1. Bobrow, D., T. Winograd, “An Overview of KRL, a Knowledge Representation Language,”Cognitive Science, Vol. 1, No. 1, January 1977.
2. Brachman, R.J., “A Structural Paradigm for Representing Knowledge,” BBN Report No. 3605, Bolt, Beranek and Newman Inc., Cambridge, Mass., 1976.
3. Brachman, R.J., H. Levesque, “Competence in Knowledge Representation,”Proc. AAAI National Conference, Pittsburgh, Penn., August 1982, pp. 189–192.
4. Cold, E.F., “A Relational Model of Data for Large Shared Data Banks,”Communications of the ACM, Vol. 13, No. 6, June 1970, pp. 377–387.
5. Collins, A., E. Warnock, N. Aiello, M. Miller, “Reasoning from Incomplete Knowledge,” in [BC75].