The Suggested Upper Merged Ontology (SUMO) and its domain ontologies form the largest formal public ontology in existence today. They are being used for research and applications in search, linguistics and reasoning. SUMO is the only formal ontology that
A. Hotho, R. Jäschke, C. Schmitz, and G. Stumme. The Semantic Web: Research and Applications, volume 4011 of Lecture Notes in Computer Science, page 411-426. Heidelberg, Springer, (June 2006)
E. Oren, M. Volkel, J. Breslin, and S. Decker. Database and Expert Systems Applications, 4080/2006, page 509-518. Springer Berlin / Heidelberg, (September 2006)