L. Wu, X. Huang, J. Niu, Y. Guo, Y. Xia, and Z. Feng. TREC, volume 500-250 of NIST Special Publication, National Institute of Standards and Technology (NIST), (2001)
C. Khoo, S. Chan, and Y. Niu. ACL '00: Proceedings of the 38th Annual Meeting on Association for Computational Linguistics, page 336--343. Morristown, NJ, USA, Association for Computational Linguistics, (2000)