“…Research on concept normalization has grown thanks to shared tasks such as disorder normalization in the 2013 ShARe/CLEF (Suominen et al, 2013), chemical and disease normalization in BioCreative V Chemical Disease Relation (CDR) Task , and medical concept normalization in 2019 n2c2 shared task (Henry et al, 2020), and to the availability of annotated data (Dogan et al, 2014;Luo et al, 2019). Existing approaches can be divided into three categories: rule-based approaches using string-matching or dictionary look-up (Leal et al, 2015;D'Souza and Ng, 2015;Lee et al, 2016), which rely heavily on handcrafted rules and domain knowledge; supervised multi-class classifiers (Limsopatham and Collier, 2016;Lee et al, 2017;Tutubalina et al, 2018;Niu et al, 2019;Li et al, 2019), which cannot generalize to concept types not present in their training data; and two-step frameworks based on a nontrained candidate generator and a supervised candidate ranker (Leaman et al, 2013;Li et al, 2017;Liu and Xu, 2017;Nguyen et al, 2018;Murty et al, 2018;Mondal et al, 2019;Ji et al, 2020;Xu et al, 2020), which require complex pipelines and fail if the candidate generator does not find the gold truth concept.…”