Dependency treebanks: methods, annotation schemes and tools

Abstract In this paper, current dependency-based treebanks are introduced andanalyzed. The methods used forbuilding the resources, the annotationschemes applied, and the tools used(such as POS taggers, parsers and an-notation software) are discussed. 1 Introduction Annotated data is a crucial resource for devel-opments in computational linguistics and nat-ural language processing. Syntactically anno-tated corpora, treebanks, are needed for de-veloping and evaluating natural language pro-cessing applications, as well as for researchin empirical linguistics. The choice of annota-tion type in a treebank usually boils down totwo options: the linguistic resource is anno-tated either according to some constituent orfunctional structure scheme. As the name tree-bank suggests, these linguistic resources wereﬁrst developed in the phrase-structure frame-work, usually represented as tree-shaped con-structions. The ﬁrst efforts to create such re-sources started around 30 years ago. The mostwell-known of such a treebank is the Penn Tree-bank for English (Marcus et al., 1993). In recent years, there has been a wide in-terest towards functional annotation of tree-banks. In particular, many dependency-basedtreebanks have been constructed. In addi-tion, grammatical function annotation has beenadded to some constituent-type treebanks. De-pendency Grammar formalisms stem from thework of Tesnieere (1959). In dependency gram-mars, only the lexical nodes are recognized,and the phrasal ones are omitted. The lexi-cal nodes are linked with directed binary re-lations. The most commonly used argumentfor selecting the dependency format for build-ing a treebank is that the treebank is beingcreated for a language with a relatively freeword order. Such treebanks exist e.g. forBasque, Czech, German and Turkish. On theother hand, dependency treebanks have beendeveloped for languages such as English, whichhave been usually seen as languages that canbe better represented with constituent formal-ism. The motivations for using dependency an-notation vary from the fact that the type ofstructure is the one needed by many, if notmost, applications to the fact that it offers aproper interface between syntactic and seman-tic representation. Furthermore, dependencystructures can be automatically converted intophrase structures if needed (Lin, 1995; Xiaand Palmer, 2000), although not always with100% accuracy. The TIGER Treebank of Ger-man, a free word order language, with 50,000sentences is an example of a treebank withboth phrase structure and dependency annota-tions (Brants et al., 2002). The aim of this paper is to answer the follow-ing questions about the current state-of-art independency treebanking:• What kinds of texts do the treebanks con-sist of? • What types of annotation schemes and for-mats are applied? • What kinds of annotation methods andtools are used for creating the treebanks? • What kinds of functions do the annotationtools for creating the treebanks have? We start by introducing the existingdependency-based treebanks (Section 2). In Section 3, the status and state-of-art independency treebanking is summarized and