S. Xu, S. Bao, B. Fei, Z. Su, and Y. Yu. Proceedings of the 31st annual international ACM SIGIR conference on Research and development in information retrieval, page 155--162. New York, NY, USA, ACM, (2008)
H. Wu, M. Zubair, and K. Maly. HYPERTEXT '06: Proceedings of the seventeenth conference on Hypertext and hypermedia, page 111--114. New York, NY, USA, ACM Press, (2006)