BKTreebank: Building a Vietnamese Dependency Treebank

BKTreebank: Building a Vietnamese Dependency Treebank Kiem-Hieu Nguyen School of information and communication technology, Hanoi university of science and technology, 1 Dai Co Viet, Bach Khoa, Hai Ba Trung, Hanoi, Vietnam hieunk@soict.hust.edu.vn Abstract Dependency treebank is an important resource in any language. In this paper, we present our work on building BKTreebank, a dependency treebank for Vietnamese. Important points on designing POS tagset, dependency relations, and annotation guidelines are discussed. We describe experiments on POS tagging and dependency parsing on the treebank. Experimental results show that the treebank is a useful resource for Vietnamese language processing. Keywords: treebank, dependency parsing, POS tagging, word segmentation, Vietnamese, less-resourced language 1. Introduction Dependency treebank is important for data-driven depen- dency parsing. However, building a dependency treebank is complicated and expensive. Dependency treebanks have been available in English and many languages. VnDT (Nguyen et al., 2014) is a Viet- namese dependency treebank which was automatically converted from tree bracketing in VietTreebank (VTB) (Nguyen et al., 2009; Nguyen et al., 2015). In this work, we present the building of a dependency tree- bank for Vietnamese1. Our treebank was manually anno- tated by annotators. Its annotation guidelines substantially differ from VTB. Our contributions are two-fold: • A manual dependency treebank for Vietnamese. • Experiments on POS tagging and dependency parsing based on the treebank. The paper is organized as follows: Section 2. briefly intro- duces related work on building treebanks for Vietnamese and dependency treebanks for other languages. Section 3. highlights important points of annotation guidelines. Sec- tion 4. describes in brief the annotation process. Section 5. is dedicated to evaluations and discussions on automatic POS tagging and dependency parsing results. The paper is concluded in Section 6. 2. Related Work 2.1. Treebanks for Vietnamese VTB was the pioneer treebank for Vietnamese. It has been developed from 2006-2010. It contains manual annotations on about 40K sentences for word segmentation, 10K sen- tences for POS tagging, and 10K sentences for bracketing. VnDT contains dependency annotations which were auto- matically converted from bracketing annotations in VTB. State-of-the-art performance on VnDT is 80.7% and 73.5% on UAS and LAS, respectively (Nguyen et al., 2016a). Recently, a new treebank for Vietnamese has been devel- oped (Nguyen et al., 2016b; Nguyen et al., 2017). It con- sists of 40K sentences annotated with word segmentation, 1For information on using BKTreebank, please visit http://is.hust.edu.vn/˜hieunk/bktreebank/ POS tagging, and bracketing. While generally agreeing on word segmentation and bracketing, they propose a POS tagset and POS tagging guidelines which focus more on word-class transformation, particularly between verbs and other word-classes. This issue is important as Vietnamese is an analytic language. Unfortunately, their treebank has not been publicly available for research community yet. 2.2. Dependency treebank for other languages One of the most notable dependency treebanks for English was developed by Stanford NLP group (De Marneffe and Manning, 2008). The Stanford treebank is automatically converted from PeenTreebank phrase structures (Marneffe et al., 2006). Similar approaches were used to build de- pendency treebanks in other languages such as …

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