1. N. Guarino, Formal ontology and information systems, in: N. Guarino (Ed.), Formal Ontology in Information Systems, Proceedings of FOIS 1998, IOS Press, Amsterdam, 1998.
2. Available on-line at: 〈http://www.jfsowa.com/ontology/ontoshar.htm〉.
3. Available on-line at: 〈http://ontology.buffalo.edu/ontology(PIC).pdf〉.