Hiroshi Ichikawa Keita Hakoda Taiichi Hashimoto Takenobu Tokunaga Efficient Sentence Retrieval Based on Syntactic Structure. 2006 conf/acl/2006 ACL http://acl.ldc.upenn.edu/P/P06/P06-2052.pdf db/conf/acl/acl2006.html#IchikawaHHT06