Dependency Treebank : From analytic to tectogrammatical annotations

The Prague Dependency Treebank is conceived of as an annotated corpus of written Czech, comprising three layers of annotations. In the present paper, we focus on a more detailed description of the structure and contents of the tectogrammatical syntactic trees (underlying sentence representations) and a specification of the transition from the analytic syntactic tree to the tectogrammatical one. 1. An Overview of the Prague Dependency Treebank The project called The Prague Dependency Tree Bank (PDT) was inspired by the activities resulting in the Penn Treebank: the aim is to achieve a complex annotation of (a part of) the Czech National Corpus (CNC), the creation of which is under progress at the Department of Czech National Corpus at the Faculty of Philosophy, Charles University (the corpus currently comprises about 70 million tokens or word forms) so that the corpus (or at least a representative part of it) would contain not only data on part-of-speech appurtenance of the individual lexical occurrences, but also information on grammatical (syntactic) values. The annotation scheme of PTB works with three layers of tagging: (1) Morphological (POS) tagging (with more than 3000 labels) including disambiguated lemmas (described in detail in Hajič & Hladká, 1997). (2) Analytic syntactic tagging (see Hajič, 1998) the result of which are dependency trees with nodes labelled (in addition to the POS tags and lemmas, see (1) above) by the word forms together with tags representing the syntactic relations; the analytic layer is conceived of as a step towards (underlying, tectogrammatical) syntactic representations and in the current phase of the project, about 30000 Czech sentences taken from the corpus have been annotated manually on this layer. (3) Tectogrammatical tagging, resulting in dependency trees the nodes of which are labelled by the autosemantic lexical items of the sentence with tags representing the syntactico-semantic (tectogrammatical, TR's, in the sense of the Functional Generative Description, see e.g. Sgall et al., 1986) relations such as Actor/Bearer, Patient, Addressee, Effect, Origin, and circumstantial modifications of different kinds. 2. The Tectogrammatical Layer of Annotations The form of the tectogrammatical syntactic trees (TSTs) is basically conceived of in accordance with the theoretical assumptions of FGD. The TSTs have the shape of a dependency tree with the verb as the root of the tree and its daughter nodes representing nodes depending on the governor (on each layer of the tree). The two dimensions of the tree represent the syntactic structure of the sentence (the vertical dimension) and the topic-focus articulation of the sentence, based on the underlying word order (the horizontal dimension). In comparison to the analytic trees, the TSTs are guided by the following principles: (a) a single node of a TST may be a representation of more than one word; only autosemantic words have a node of their own, while the correlates of functional words (auxiliaries, prepositions etc.) are attached as indices to the autosemantic words to which they "belong" (auxiliaries and conjunctions to lexical verbs, prepositions to nouns, etc.); (b) nodes are added in case of clearly specified deletions on the surface level; (c) non-projectivity (i.e. crossing of edges with each other or with perpendiculars incident to nodes) is not allowed; (d) analytic functions are substituted by tectogrammatical functions (such as Actor/Bearer, Patient, Addressee, Origin, Effect, different kinds of Circumstantials); (e) at least some basic features of the information structure of the sentences (Topic-Focus Articulation) are added. The tentative and preliminary inventory of the tectogrammatical labels (based on the detailed studies of Sgall, 1967; Sgall et al., 1986; Petkevič, 1995) comprises 10 grammatemes (i.e. attributes taking as their value the values of morphological categories such as Tense, Modality, Aspect etc.) and 47 functors (i.e. syntactic relations). 3. The transition from the analytic to the tectogrammatical layer of tagging To illustrate the two syntactic layers of tagging briefly characterized above, we present in Figs. 1 and 2 the analytic syntactic tree and the tectogrammatical syntactic tree of sentence (1) as taken from our corpus (sentence No. 22); for the sake of transparency, we omit the POS tags in both trees and add only the grammatemes of modalities and the functors in the TST. (1) Vechny domy musí být stavěny s kryty , ale dosud All houses must be built with shelters, but hitherto pouze proti konvenčnímu útoku . only against conventional attack.