Wojood: Nested Arabic Named Entity Corpus and Recognition using BERT
Summary
Arabic NER resources had so far been annotated only with flat labels. This means an entity sitting inside another one is lost: a city name inside a university name, or a person's name inside an organization's name. Nested NER also gets little attention in general, mostly because there is not enough data. The authors address this gap with Wojood, a manually annotated corpus of roughly 550K tokens. It covers Modern Standard Arabic and dialectal text from many domains: web articles on health, finance, law, elections, migration and similar topics, plus documents from the Awraq Palestinian historical archive. Annotators labelled 21 entity types and allowed up to four nesting layers. Agreement between annotators was very high.
To show that the data can be learned from, the authors fine-tuned AraBERT in a multi-task setup that predicts the nested tags. It reached a micro F1 of 0.884. Wojood is the first nested NER corpus for Arabic, and it is also larger and broader than earlier flat corpora such as ANERCorp and Ontonotes 5. The corpus, guidelines, code and model are publicly released, and the model is also served as a web service.
Key points
- Wojood has about 550K tokens and around 75K entity mentions. About 22.5% of these mentions are nested inside another mention, with up to four nesting layers.
- Among the corpus's 21 entity types are date, event, location, organization and person. It contains both MSA and dialect text, tagged with the IOB2 scheme.
- The sources are about 258K tokens of web articles (un.org, hrw.org, who.org, quora.com and others) and about 227K tokens from the Awraq archive of Birzeit University.
- Inter-annotator agreement reached Cohen's Kappa 0.979 and F1 0.976.
- The multi-task fine-tuned AraBERT model scored a micro F1 of 0.884. The corpus, guidelines, code and model are public.
Interesting ideas
- I1. Annotating embedded entities rather than flattening them keeps facts such as "this organization is named after a place/person" recoverable from the labels themselves. — For Mova (world): the entity store could keep inner mentions of a name as linked entities, e.g. a GPE inside an ORG, so the world graph gets a free "located in" or "named after" hint.
- I2. Nested tagging can be treated as several parallel sequence-labelling tasks on one shared pre-trained encoder, which avoids a heavy recursive decoder. — For Mova (tree): gparse's transformer encoder could carry extra cheap tagging heads, such as entity layers, next to the dependency head, so both use one forward pass.
- I3. Annotation quality is reported twice: as a chance-corrected Kappa and as an F1 over mentions. The second number shows span-level disagreement that the first one can hide. — For Mova (learn): agreement among the witness parsers on silver data could be scored the same way, using both a chance-corrected statistic and an arc/label F1, to decide which trees to trust.
- I4. A surveyed approach (Ju et al.) stacks flat tagging layers and stops once a layer outputs only "O". This gives a natural, data-driven depth for nested structure. — For Mova (tokens): a named-entity chunker could peel nested names layer by layer with the same stopping rule, keeping each layer explainable.
- I5. The new corpus is validated by training a model on it and reporting the score, and it is released together with the guidelines and code. — For Mova (learn): every new silver treebank could ship with a "train the parser on it and evaluate" check, plus its written conversion rules, before it is admitted to training.
Cited by
- Integrating AI into Arabic Linguistics: A Methodological Framework for Reproducible and Interpretable Research
- SinaTools: Open Source Toolkit for Arabic Natural Language Processing
- Lisan: Yemeni, Iraqi, Libyan, and Sudanese Arabic Dialect Copora with Morphological Annotations
- Offensive Hebrew Corpus and Detection using BERT
- Masrad: Arabic Terminology Management Corpora with Semi-Automatic Construction
Cite
@inproceedings{jarrar2022wojood,
title = {{Wojood: Nested Arabic Named Entity Corpus and Recognition using BERT}},
author = {Jarrar, Mustafa and Khalilia, Mohammed and Ghanem, Sana},
booktitle = {Proceedings of the Thirteenth Language Resources and Evaluation Conference},
year = {2022},
doi = {10.63317/57rz4w3or4jm},
url = {https://doi.org/10.63317/57rz4w3or4jm}
}References
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