Uniform Resource Name. A more stable identifier than a locator. (Names do change, but less often than addresses).
URNs need to be resolved to addresses, if they live on the web. A DOI is a URN. DOI registrars like CrossRef keep track of the URL of the URN called “DOI” so that it resolves. (Because URN is a standard and DOIs don’t adhere to it, doi.org refuses to call its DOIs “URNs”).
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