The SCOT(Social Semantic Cloud Of Tags) ontology is to semantically represent the structure and semantics of a collection of tags and to represent social networks among users based on the tags.
S. Jeffery, M. Franklin, and A. Halevy. Proceedings of the 2008 ACM SIGMOD international conference on Management of data, page 847--860. New York, NY, USA, ACM, (2008)
S. Tramp, P. Frischmuth, T. Ermilov, and S. Auer. Proceedings of the EKAW 2010 - Knowledge Engineering and Knowledge Management by the Masses; 11th October-15th October 2010 - Lisbon, Portugal, volume 6317 of Lecture Notes in Artificial Intelligence, page 135--149. Berlin / Heidelberg, Springer, (October 2010)