1. Newell A. The knowledge level. Artificial Intelligence 1982; 18: 87–127
2. Gruber T.R. A translation approach to portable ontology specifications. Knowledge Acquisition 1993; 5: 199–220
3. Sowa J. Top-leyel ontological categories. International Journal of Human-Computer Studies 1995; 43(5/6): 669–686 Studer R, Benjamins V.R, Fensel D. Knowledge Engineering: Principles and Methods. Data & Knowledge Engineering 1998; 25: 161–197
4. Dahlgren K. Naive semantics for natural language understanding. Kluwer Academic, Boston, MA, 1988
5. Karp P.D. Hunter L. A qualitative biochemistry and its application to the regulation of the trytophan operon. In: Artificial Intelligence and Molecular Biology. AAAI Press/The MIT Press, 1993, pp. 289–325