Ciro Cattuto wrote a simple piece of code that builds and visualizes a network of inferred semantic relations among the tags that Flickr users attach to their photos.
official website of the TAGora project, a STREP project funded by the European Commission in the framework of the FET proactive initiative “Simulating Emergent Properties in Complex Systems”
G. Little, L. Chilton, M. Goldman, and R. Miller. HCOMP '09: Proceedings of the ACM SIGKDD Workshop on Human Computation, page 29--30. New York, NY, USA, ACM, (2009)