Defined in file biblio.asn
C++ class: CArticleId
ArticleId ::= CHOICE { -- can be many ids for an article
pubmed PubMedId , -- see types below
medline MedlineUID ,
doi DOI ,
pii PII ,
pmcid PmcID ,
pmcpid PmcPid ,
pmpid PmPid ,
other Dbtag } -- generic catch all