An Annotation Scheme for Free Word Order Languages

An Annotation Scheme for Free Word Order Languages Wojciech Skut, Brigitte Krenn, Thorsten Brants, Hans Uszkoreit Universit/~t des Saarlandes 66041 Saarbrficken, Germa,ny { skut, krenn, brant s, uszkore±t }@col ±. un±- sb. de Abstract We describe an annotation scheme and a tool developed for creating linguistically annotated corpora for non-configurational languages. Since the requirements for such a formalism differ from those posited for configurational languages, several featu- res have been added, influencing the ar- chitecture of the scheme. The resulting scheme reflects a stratificational notion of language, and makes only minimal assump- tions about the interrelation of the particu- Jar representational strata. 1 Introduction The work reported in this paper aims at provi- ding syntactically annotated corpora ('treebanks') for stochastic grammar induction. In particular, we focus on several methodological issues concerning the annotation of non-configurational languages. In section 2, we examine the appropriateness of existing annotation schemes. On the basis of these considerations, we formulate several additional re- quirements. A formMism conrplying with these re- quirements is described in section 3. Section 4 deals with the treatment of selected phenomena. For a description of the annotation tool see section 5. 2 Motivation 2.1 Linguistically Interpreted Corpora Combining raw language data with linguistic intor- mation offers a promising basis for the development of new efficient and robust NLP methods. Real- world texts annotated with difihrent strata of lin- guistic information can be used for grarninar indue- tion. The data-drivenness of this approach presents a clear advantage over tile traditional, idealised no- tion of competence grammar. 2.2 Existing Treebank Formats Corpora annotated with syntactic structures are commonly referred to as trt:tbauk.~. Existing tree- bank annotation schemes exhibit a fairly uniform architecture, as they all have to meet the same basic requirements, namely: Descriptivity: GrammaticM phenomena are to be described rather than explained. Theory-independence: Annotations should not be influenced by theory-specific considerations. Nevertheless, different theory-specific represen- tations shMl be recoverable from the annota- tion, cf. (Marcus et al., 1994). Multi-stratal representation: Clear separation of different description levels is desirable. Data-drivenness: The scheme must provide repre- sentational means for all phenomena occurring in texts. Disambiguation is based on human processing skills (cf. (Marcus et at., 1994), (Sampson, 1995), (Black et al. , 1996)). The typical treebank architecture is as follows: Structures: A context-free backboI~e is augmented with trace-filler representations of non-local de- pendencies. The underlying argum~.nt structure is not represented directly, but can be recovered from the tree and trace-filler ammtations. Syntactic category is encoded in node IM:,els. Gralnmatical flinctioxls constitute a complex la- bel system (cf. (Bies et al., 1995), (Sampson, 1995)). Part-of-Speech is annotated at word level. Thus the context-li'ee constituent backbone plays a pivotal role in the annotation scherne. Due to the substantial differences between existing models of constituent structure, tile question arises of how the theory indcp~ndcnc~, requirement can be satis- fied. At this point the mlportance of the underlying argument struc~ur¢: is emphasised (cf. (Lehmaim et al., 1996), (Marcus et al., 1994), (Sampson, 1995)). 2.3 Language-Specific Features Treebanks of …

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