S. Auer, C. Bizer, G. Kobilarov, J. Lehmann, R. Cyganiak, and Z. Ives. Proceedings of the 6th International Semantic Web Conference (ISWC), volume 4825 of Lecture Notes in Computer Science, page 722--735. Springer, (2008)
S. Braun, A. Schmidt, A. Walter, and V. Zacharias. Good Tags and Bad Tags - Social Tagging in der Wissensorganisation, volume 47 of Medien in der Wissenschaft, Waxmann, (2008)