HiCo-EL: Encoding Ontology Structure into Bi-Encoder Entity Linking

Albert Lee, Prasanth Bathala, Puru Malhotra, Christophe Ye, Cassie S. Mitchell


Abstract
Bi-encoder architectures for biomedical entity linking learn flat embedding spaces that ignore ontology structure. HiCo-EL encodes hierarchical knowledge into bi-encoder representations through hierarchical contrastive pretraining. The core idea is within-space hierarchical multi-label contrastive learning (HMLC): contrastive losses applied independently within each encoder space, preserving cross-space compatibility for retrieval. Our formulation drops the monotonicity constraints of prior HMLC work, handles variable-depth hierarchy paths, and adds depth-weighted alignment between encoder spaces. Treating each entity as a leaf node unifies coarse type structure with fine-grained entity discrimination. On MedMentions and NCBI Disease, HiCo-EL outperforms ArboEL by +3.7% and +1.8% Recall@1 respectively. The gains reveal a key insight: breadth amplifies, depth generalizes—broad hierarchies help common entities most (+6.3% R@1), while deep hierarchies benefit unseen entities (+9.6% R@1 zero-shot).
Anthology ID:
2026.findings-emnlp.103
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
2113–2123
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.103/
DOI:
Bibkey:
Cite (ACL):
Albert Lee, Prasanth Bathala, Puru Malhotra, Christophe Ye, and Cassie S. Mitchell. 2026. HiCo-EL: Encoding Ontology Structure into Bi-Encoder Entity Linking. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 2113–2123, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
HiCo-EL: Encoding Ontology Structure into Bi-Encoder Entity Linking (Lee et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.103.pdf