M. Anderka, B. Stein, und N. Lipka. Proceedings of the 20th ACM international conference on Information and knowledge management, Seite 2313--2316. New York, NY, USA, ACM, (2011)
K. Chen, T. Chen, G. Zheng, O. Jin, E. Yao, und Y. Yu. Proceedings of the 35th international ACM SIGIR conference on Research and development in information retrieval, Seite 661--670. ACM, (2012)