@inproceedings{Zhu:2011:IJCNLP,
     title = "Indexing Spoken Documents with Hierarchical Semantic Structures: Semantic Tree-to-string Alignment Models",
     author = "Zhu, Xiaodan and Cherry, Colin and Penn, Gerald",
     booktitle = "Proceedings of International Joint Conference on Natural Language Processing",
     year = "2011",
     location = "Chiangmai, Thailand",
}