NARC – N orwegian Anaphora Resolution Corpus (2022)

Abstract: We present the Norwegian Anaphora Resolution Corpus (NARC), the first publicly available corpus annotated with anaphoric relations between noun phrases for Norwegian. The paper describes the annotated data for 326 documents in Norwegian Bokmål, together with inter-annotator agreement and discussions of relevant statistics. We also present preliminary modelling results which are comparable to existing corpora for other languages, and discuss relevant problems in relation to both modelling and the annotations themselves.

## introduction coreference resolution (cr) is a central nlp task which enables a wide range of applications aiming to extract and aggregate various types of information from text, e.g. relations, events and opinions. while a number of datasets for cr have been developed for a range of different languages, no such openly available dataset is currently available for norwegian. in this paper, we describe the annotation of the norwegian anaphora resolution corpus (narc). the annotation effort enriches the existing annotation of the norwegian dependency treebank (ndt) @xcite , which has been converted to the universal dependencies standard @xcite and has further been annotated with named entities in a separate effort, resulting in the norne dataset @xcite . norwegian has two written standards: bokmål and nynorsk, and the dataset consists of 300,000 tokens from each. 2 the paper is organized as follows: we start out by reviewing related work, then we describe the annotation effort, summarize the annotation procedure, explain guidelines developed for the project and the inter-annotator agreement scores. finally, corpus statistics and initial experiments with norwegian cr are presented, before concluding the paper. ## related work in this section we review some related work, both in terms of existing datasets with coreference annotation and research on coreference modelling based on these datasets. ## annotation we here detail the annotation effort and present the underlying data for annotation, the pre-annotation of markables, the annotated narc mentions and relations, as well as the review and curation process and inter-annotator agreement. ## corpus statistics clusters are collections of relations that have markables in common. the average length for coreference clusters is 4.7 tokens, while for bridging it is 2 tokens. most clusters, regardless of type, are of length 2, i.e. from a single antecedent to an anaphoric or bridging expression. despite the low average, there are still some very long clusters. finally, we also analyzed the data to investigate what types of expressions occur as anaphoric expressions. as noted earlier, there are primarily two types of relations that fall under coreference. the most common coreference expressions are pronouns, but both true anaphoric pronouns and pronouns referring to repeated entities are common. about 38% of all coreference relations are from a pronoun. as only third person pronouns and definite nouns can give rise to bridging relations, this is naturally reflected in the types of expressions found. the most common is the pronoun de 'they', but another notable feature of the bridging relations is that we see word forms such as hodet 'the head' øynene 'the eyes' hånden 'the hand' and skuldrene 'the shoulders' among the most common words. these are all typical of inalienable body parts, a type of bridging mentioned specifically in bredt @xcite . ## experiments this section presents preliminary benchmarking experiments on the new dataset. below we describe the distribution format of the data, the framework used for modelling and evaluation, and the results. ## conclusion this paper has introduced a new corpus for coreference resolution: the norwegian anaphora resolution corpus (narc). it is the first openly available corpus of this kind for norwegian and represents the result of a large annotation effort which en-riches the norwegian dependency treebank @xcite with annotation of document-level coreference resolution, including the annotation of split antecedents and bridging. the paper has detailed the annotation effort, including a summary of guidelines, annotion procedure, inter-annotator agreement and resulting dataset statistics, as well as provided results from initial modelling experiments. while this paper focuses on the annotation of the bokmål section of the corpus, the final corpus will contain the full treebank dataset, including also its nynorsk sections, corresponding to the second written standard of norwegian. narc, including the annotation guidelines, will be made freely available 9 . it will further be aligned with the underlying treebank, allowing for smooth interaction with the other annotation layers such as pos, dependency syntax and named entities, thus constituting a richly annotated resource for norwegian nlp in the future.