Building an Ellipsis-aware Chinese Dependency Treebank for Web Text

Building an Ellipsis-aware Chinese Dependency Treebank for Web Text Xuancheng Ren1,2, Xu Sun1,2, Ji Wen1,2, Bingzhen Wei1,2, Weidong Zhan1,3, Zhiyuan Zhang1,2 1MOE Key Laboratory of Computational Linguistics, Peking University 2School of Electronics Engineering and Computer Science, Peking University 3Department of Chinese Language and Literature, Peking University Beijing, China {renxc, xusun, wenjics, weibz, zwd, zzy1210}@pku.edu.cn Abstract Web 2.0 has brought with it numerous user-produced data revealing one’s thoughts, experiences, and knowledge, which are a great source for many tasks, such as information extraction, and knowledge base construction. However, the colloquial nature of the texts poses new challenges for current natural language processing techniques, which are more adapt to the formal form of the language. Ellipsis is a common linguistic phenomenon that some words are left out as they are understood from the context, especially in oral utterance, hindering the improvement of dependency parsing, which is of great importance for tasks relied on the meaning of the sentence. In order to promote research in this area, we are releasing a Chinese dependency treebank of 319 weibos, containing 572 sentences with omissions restored and contexts reserved. Keywords: ellipsis, dependency treebank, web text 1. Introduction With the rapid development of Web 2.0, the internet pro- vides us with numerous raw text, which is a great source for structured learning such as information extraction. How- ever, the information in Web 2.0 is usually highly unstruc- tured and of various forms, written in a more casual way, which makes it hard to directly apply techniques that works for regular text. One probable way to structure the text is through syntax parsing, which exposes the syntax relation, and implicitly semantic relation, between words, especially dependency parsing (Tesni`ere, 1959). However, due to the different construction of the sentences in web text, the cur- rent parsing methods face greatly challenge (K¨ubler et al., 2009; Petrov and McDonald, 2012). Web text usually rep- resents more of a spoken language aspect than the writ- ten language aspect, which means the social effect is more dominant in its formation, and the efficiency in conveying the information is more valued. In this work, we focus on building a resource to facilitate the parsing of the web text, specifically text from online microblogs. A common issue of the current techniques is that they lack the ability to deal with omitted elements in the text, which are more often referred as ellipsis in linguistics. Ellipsis is a common linguistic phenomenon across languages, which facilitates the communication in real-world conversations, as the omitted elements should be understood from the con- text. The down side is that the sentence is often made less structured, and cannot easily be understood if extracted from the context. This work is a first step towards estab- lishing a more robust parsing framework through recogniz- ing the ubiquitous ellipsis in web text and identifying the omitted elements from such type of sentences. We build a Chinese dependency treebank based on the messages ex- The treebank is available at https://github.com/ lancopku/Chinese-Dependency-Treebank-with- Ellipsis. tracted …

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