Prague Dependency Treebank: Restoration of Deletions

The use of the treebank as a resource for linguistic research has led us to look for an annotation scheme representing not only surface syntactic information (in ‘analytic trees’, ATS) but also the underlying syntactic structure of sentences and at least some aspects of intersentential links (in ‘tectogrammatical tree structures’, TGTS). We focus in this paper on some of the issues of the transduction of ATSs into TGTSs. 1 Two steps of syntactic tagging in PDT In the Prague Dependency Treebank (PDT) project, the structure of sentences is made explicit by means of two steps of syntactic tagging resulting in: (i) ‘analytic’ tree structures (ATSs), in which every word form and punctuation mark is represented as a node of the tree, and the edges of the tree correspond to (surface) syntactic dependency relations; and, (ii) tectogrammatical tree structures (TGTSs) corresponding to underlying sentence representations and having the shape of dependency trees with the verb as the root of the tree.1 In TGTSs the functional (synsemantic) words (such as prepositions, auxiliaries, subordinating conjunctions) as well as punctuation marks are principally not represented by nodes of their own; their functions are captured as parts of complex tags of the nodes standing for autosemantic (content) words. Surface deletions are ‘restored’ in TGTSs. The syntactic information which is absent in the surface (morphemic) shape of the sentence is introduced at least for the time being in the manual phase of the transduction procedure ([Hajičová et al. 1998]), translating (in a ‘userfriendly’ environment) ATSs to TGTSs. Every added (restored) node gets the index ELEX (if its antecedent is an expanded head node) or ELID (if this is not so). The added nodes always depend on their governors from the left-hand side, except for certain cases in coordinated constructions (cf. (2) below). ? The work reported on in this paper has been supported by the grant of the Czech Ministry of Education VS 96/151 and by the Czech Grant Agency GAČR 405/96/K214. 1 With the exception of TGTSs for coordinated constructions, see below.