C. Marshall, and S. Bly. JCDL '04: Proceedings of the 4th ACM/IEEE-CS joint conference on Digital libraries, page 218--227. New York, NY, USA, ACM Press, (2004)
S. Bao, G. Xue, X. Wu, Y. Yu, B. Fei, and Z. Su. Proceedings of the 16th International Conference on World Wide Web, page 501--510. New York, NY, USA, ACM, (2007)