HDT-UD: A very large Universal Dependencies Treebank for German

We report on the conversion of the Hamburg Dependency Treebank (Foth et al., 2014) to Universal Dependencies. The HDT consists of more than 200.000 sentences annotated with dependency structure, making every attempt at manual conversion or manual post-processing extremely costly. The conversion employs an unranked tree transducer. This formalism allows to express transformation rules in a concise way, guarantees the well-formedness of the output and is predictable to the rule writers. Together with the release of a converted subset of the HDT spanning 3 million tokens, we release an interactive workbench for writing and refining tree transducer rules. Our conversion achieves a very high labeled accuracy with respect to a manually converted gold standard of 97.3%. Up to now, the conversion effort took about 1000 hours of work.