TIGER Transfer—Utilizing LFG Parses for Treebank Annotation

Creation of high-quality treebanks requires expert knowledge and is extremely time consuming. Hence applying an already existing grammar in treebanking is an interesting alternative. This approach has been pursued in the syntactic annotation of German newspaper text in the Tiger project. We utilized the large-scale German LFG grammar of the ParGram project for semi-automatic creation of Tiger treebank annotations. The symbolic LFG grammar is used for full parsing, followed by semi-automatic disambiguation and automatic transfer into the treebank format. The treebank annotation format is a `hybrid' representation structure which combines constituent analysis and functional dependencies. Both types of information are provided by the LFG analyses.

Although the grammar and the treebank representations coincide in core aspects, e.g. the encoding of grammatical functions, there are mismatches in analysis details that are comparable to translation mismatches in natural language translation. This motivates the use of transfer technology from machine translation.

The German LFG grammar analyzes on average 50% of the sentences, roughly 70% thereof are assigned a correct parse; after OT-filtering, a sentence gets 16.5 analyses on average (median: 2). We argue that despite the limits in corpus coverage the applications of the grammar in treebanking is useful especially for reasons of consistency. Finally, we sketch future extensions and applications of this approach, which include partial analyses, coverage extension, annotation of morphology, and consistency checks.