Aligning the Norwegian UD Treebank with Entity and Coreference Information

TL;DR

The work addresses the lack of up-to-date Norwegian coreference baselines by merging UD Bokmål and Nynorsk with NorNE and NARC into a unified, CoNLL-U-annotated resource. A conversion and alignment pipeline (BRAT -> JSONL -> CoNLL-U) is developed, and UD-NARC sentence alignment is solved via a cost-minimizing linear assignment, leveraging UD version $2.12$. The authors report thorough error analyses and data-loss metrics from alignment, identifying tokenization mismatches, duplicates, lemma injections, and data-split overlaps. The resulting modular workflow and codebase (UD-NARC) provide a reusable foundation for future corpus alignment tasks and enable coreference-enriched Norwegian UD resources.

Abstract

This paper presents a merged collection of entity and coreference annotated data grounded in the Universal Dependencies (UD) treebanks for the two written forms of Norwegian: Bokmål and Nynorsk. The aligned and converted corpora are the Norwegian Named Entities (NorNE) and Norwegian Anaphora Resolution Corpus (NARC). While NorNE is aligned with an older version of the treebank, NARC is misaligned and requires extensive transformation from the original annotations to the UD structure and CoNLL-U format. We here demonstrate the conversion and alignment processes, along with an analysis of discovered issues and errors in the data - some of which include data split overlaps in the original treebank. These procedures and the developed system may prove helpful for future corpus alignment and coreference annotation endeavors. The merged corpora comprise the first Norwegian UD treebank enriched with named entities and coreference information.