7th International Conference on Spoken Language Processing

September 16-20, 2002
Denver, Colorado, USA

Selective Back-Off Smoothing for Incorporating Grammatical Constraints into the N-Gram Language Model

Tomoyosi Akiba (1), Katunobu Itou (1), Atsushi Fujii (2), Tetsuya Ishikawa (2)

(1) National Institute of Advanced Industrial Science and Technology, Japan; (2) University of Library and Information Science, Japan

Spoken queries submitted to question answering systems usually consist of query contents (e.g. about newspaper articles) and frozen patterns (e.g. WH-words), which can be modeled with N-gram models and grammar-based models, respectively. We propose a method to integrate those different types of models into a single N-gram model. We represent the two types of language models in a single word network. However, common smoothing methods, which are effective for N-gram models, decrease grammatical constraints for frozen patterns. For this problem, we propose a selective back-off smoothing method, which controls a degree to which smoothing is applied depending the network fragment. Additionally, resulting models are compatible with the conventional back-off N-gram models, and thus existing N-gram decoders can easily be used. We show the effectiveness of our method by way of experiments.

Full Paper

Bibliographic reference.  Akiba, Tomoyosi / Itou, Katunobu / Fujii, Atsushi / Ishikawa, Tetsuya (2002): "Selective back-off smoothing for incorporating grammatical constraints into the n-gram language model", In ICSLP-2002, 881-884.