Now, the real breakthru of folksonomical-based systems like del.icio.us or flickr is not the lack of structure or commitee-based design in the ontological space, but is the idea that if two people use the same term, it's more probable than they meant the same thing than they meant different things.
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J. Mueller, S. Doerfel, M. Becker, A. Hotho, und G. Stumme. Recommender Systems and the Social Web Workshop at 7th ACM Conference on Recommender Systems, RecSys 2013, Hong Kong, China -- October 12-16, 2013. Proceedings, 1066, Aachen, Germany, CEUR-WS, (2013)