1. Web 2.0, www.citeulike.org , www.delicious.com , www.flickr.com , www.last.fm
2. Yildirim, H., Krishnamoorthy, M.S.: A random walk method for alleviating the sparsity problem in collaborative filtering. In: RecSys, pp. 131–138 (2008)
3. Cattuto, C., Benz, D., Hotho, A., Stumme, G.: Semantic analysis of tag similarity measures in collaborative tagging systems. In: OLP3, pp. 39–43 (2008)
4. Zanardi, V., Capra, L.: Social ranking: uncovering relevant content using tag-based recommender systems. In: RecSys, pp. 51–58 (2008)
5. Bender, M., Crecelius, T., Kacimi, M., Miche, S., Xavier Parreira, J., Weikum, G.: Peer-to-peer information search: Semantic, social, or spiritual? TCDE 30(2), 51–60 (2007)