Learning Nested Named Entity Recognition from Flat Annotations

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Hauptverfasser: Rozhkov, Igor, Loukachevitch, Natalia
Format: Preprint
Veröffentlicht: 2026
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author Rozhkov, Igor
Loukachevitch, Natalia
author_facet Rozhkov, Igor
Loukachevitch, Natalia
contents Nested named entity recognition identifies entities contained within other entities, but requires expensive multi-level annotation. While flat NER corpora exist abundantly, nested resources remain scarce. We investigate whether models can learn nested structure from flat annotations alone, evaluating four approaches: string inclusions (substring matching), entity corruption (pseudo-nested data), flat neutralization (reducing false negative signal), and a hybrid fine-tuned + LLM pipeline. On NEREL, a Russian benchmark with 29 entity types where 21% of entities are nested, our best combined method achieves 26.37% inner F1, closing 40% of the gap to full nested supervision. Code is available at https://github.com/fulstock/Learning-from-Flat-Annotations.
format Preprint
id arxiv_https___arxiv_org_abs_2603_00840
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Learning Nested Named Entity Recognition from Flat Annotations
Rozhkov, Igor
Loukachevitch, Natalia
Computation and Language
Nested named entity recognition identifies entities contained within other entities, but requires expensive multi-level annotation. While flat NER corpora exist abundantly, nested resources remain scarce. We investigate whether models can learn nested structure from flat annotations alone, evaluating four approaches: string inclusions (substring matching), entity corruption (pseudo-nested data), flat neutralization (reducing false negative signal), and a hybrid fine-tuned + LLM pipeline. On NEREL, a Russian benchmark with 29 entity types where 21% of entities are nested, our best combined method achieves 26.37% inner F1, closing 40% of the gap to full nested supervision. Code is available at https://github.com/fulstock/Learning-from-Flat-Annotations.
title Learning Nested Named Entity Recognition from Flat Annotations
topic Computation and Language
url https://arxiv.org/abs/2603.00840