Shenghua Bao, Guirong Xue, Xiaoyuan Wu, Yong Yu, Ben Fei, und Zhong Su. Optimizing web search using social annotations. WWW '07: Proceedings of the 16th international conference on World Wide Web, ACM Press, New York, NY, USA, 2007. [PUMA: tagging taggingsurvey social bookmarking annotations search]