1. E. M. Voorhees, Overview of the TREC 2003 question answering track, in: Proc. of the Twelfth Text REtrieval Conference (TREC 2003), 2004, pp. 54–68.
2. E. M. Voorhees, Overview of the TREC 2004 question answering track, in: Proc. of the Thirteenth Text REtrieval Conference (TREC 2004), 2005, pp. 53–62.
3. J. Fukumoto, T., Kato, F. Masui, T. Mori, An overview of the 4th Question Answering Challenge (QAC-4) at NTCIR Workshop 6, in: Proc. of the Sixth NTCIR Workshop Meeting, 2007, pp. 433–440.
4. T. Kato, J., Fukumoto, F. Masui, An overview of NTCIR-5 QAC3, in: Proc. of the Fifth NTCIR Workshop Meeting, 2005, pp. 361–372.
5. S. Small, T., Strzalkowski, T. Janack, T., Liu, S. Ryan, R., Salkin, N. Shimizu, P., Kantor, D. Kelly, R. Rittman, et al., Hitiqa: Scenario based question answering, in: Proceedings of HLT, 2004.