R. Arndt, R. Troncy, S. Staab, L. Hardman, and M. Vacura. The Semantic Web, 6th International Semantic Web Conference, 2nd Asian Semantic Web Conference, ISWC 2007 + ASWC 2007, Busan, Korea, November 11-15, 2007, page 30-43. (2007)
J. Sowa. Proceedings of the Linguistic on Conceptual Structures: Logical Linguistic, and Computational Issues, 1867, page 55 - 81. Springer-Verlag London, UK, (2000)