PMID (PubMed ID) is the unique identifier for a publication's abstract in PubMed.
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A DOI (Digital Object Identifier) is a publisher’s unique identifier for a publication. The prefix http://dx.doi.org/ is presumed. Publishers may charge for access.
Kho SU, Sheth A, Bodenreider O.Automatic Identification of Individual Drugs in Death Certificates. Stud Health Technol Inform. 2019 Aug 21;264:183-187. doi: 10.3233/SHTI190208.
Deckard J, McDonald CJ, Vreeman DJ.Supporting interoperability of genetic data with LOINC. J Am Med Inform Assoc. 2015 May;22(3):621-7. doi: 10.1093/jamia/ocu012. Epub 2015 Feb 5.