Investigation of Question Classifier in Question Answering Zhiheng Huang author Marcus Thint author Asli Celikyilmaz author 2009-08 text Proceedings of the 2009 Conference on Empirical Methods in Natural Language Processing Philipp Koehn editor Rada Mihalcea editor Association for Computational Linguistics Singapore conference publication huang-etal-2009-investigation https://aclanthology.org/D09-1057/ 2009-08 543 550