Learning Chinese Bracketing Knowledge Based on a Bilingual Language Model

Learning Chinese Bracketing Knowledge Based on a Bilingual Language Model Yajuan Lü, Sheng Li, Tiejun Zhao, Muyun Yang School of Computer Science & Engineering, Harbin Institute of Technology Harbin, China, 150001 Email: {lyj,lish,tjzhao,ymy}@mtlab.hit.edu.cn Abstract This paper proposes a new method for automatic acquisition of Chinese bracketing knowledge from English-Chinese sentence- aligned bilingual corpora. Bilingual sentence pairs are first aligned in syntactic structure by combining English parse trees with a statistical bilingual language model. Chinese bracketing knowledge is then extracted automatically. The preliminary experiments show automatically learned knowledge accords well with manually annotated brackets. The proposed method is particularly useful to acquire bracketing knowledge for a less studied language that lacks tools and resources found in a second language more studied. Although this paper discusses experiments with Chinese and English, the method is also applicable to other language pairs. Introduction The past few years have seen a great success in automatic acquisition of monolingual parsing knowledge and grammars. The availability of large tagged and syntactically bracketed corpora, such as Penn Tree bank, makes it possible to extract syntactic structure and grammar rules automatically (Marcus 1993). Substantial improvements have been made to parse western language such as English, and many powerful models have been proposed (Brill 1993, Collins 1997). However, very limited progress has been achieved in Chinese. Knowledge acquisition is a bottleneck for real appication of Chinese parsing. While some methods have been proposed to learn syntactic knowledge from annotated Chinese corpus, most of the methods depended on the annotated or partial annotated data(Zhou 1997, Streiter 2000). Due to the limited availbility of Chinese annotated corpus, tests of these methods are still small in scale. Although some institutions and universities currently are engaged in building Chinese tree bank, no large scale annotated corpus has been published until now because the complexity in Chinese syntatic sturcture and the difficulty in corpus annotation (Chen 1996). This paper proposes a novel method to facilitate the Chinese tree bank construction. Based on English-Chinese bilingual corpora and better English parsing, this method obtains Chinese bracketing information automatically via a bilingual model and word alignment results. The main idea of the method is that we may acquire knowledge for a language lacking a rich collection of resources and tools from a second language that is full of them. The rest of this paper is organized as follows : In the next section, a bilingual language model is introduced. Then, a bilingual parsing method supervised by English parsing is proposed in section 2. Based on the bilingual parsing, Chinese bracketing knowlege is extracted in section 3. The evaluation and discussion are given in section 4. We conclude with discussion of future work. 1 A bilingual language model – ITG Wu (1997) has proposed a bilingual language model called Inversion Transduction Grammar (ITG), which can be used to parse bilingual sentence pairs simultaneously. We will give a brief description here. For details please refer to (Wu 1995, Wu 1997). The Inversion Transduction Grammar is a bilingual context-free grammar that …

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