Source:http://linkedlifedata.com/resource/umls/id/C2348291
NCI: A unique code used by publishers in the identification and exchange of the content of a digital object, such as a journal article, web document, or other item of intellectual property. The DOI consists of two parts: a prefix assigned to each publisher by the administrative DOI agency and a suffix assigned by the publisher that may be any code the publisher chooses. (from Online Dictionary for Library and Information Science)