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.
P. Chirita, S. Costache, W. Nejdl, and S. Handschuh. WWW '07: Proceedings of the 16th International Conference on World Wide Web, page 845--854. New York, NY, USA, ACM, (2007)
G. Mishne. WWW '06: Proceedings of the 15th International Conference on World Wide Web, page 953--954. New York, NY, USA, ACM Press, (2006)paper presented at the poster track.