6. Using a Persistent Identifier

Technically, NRS persistent identifiers are Uniform Resources Names (URNs), not Uniform Resource Locators (URLs). But the current generation of web browsers only know how to deal with URLs, not URNs. Because no web clients understand URNs, NRS persistent identifiers are encapsulated into the form of URLs that refer directly to the NRS resolution server (nrs.harvard.edu).

An NRS persistent identifier of the form:

   urn-3:authority-path:resource-name

can be turned into an actionable URL by prepending "http://nrs.harvard.edu/":

   http://nrs.harvard.edu/urn-3:authority-path:resource-name

When a persistent identifier link is clicked in a catalog record or HTML page, the browser sends a request to the resolution server. When the resolution server receives the request, it extracts the persistent identifier component (urn-3:authority-path:resource-name) from the requested URL, resolves the identifier into the proper URL for the named resource, returns the resolved URL to your browser, which then retrieves the named resource.

For example, the persistent identifier for "A Century to Celebrate":

   urn-3:RAD.ARCH:15009

is turned into an actionable URL:

   http://nrs.harvard.edu/urn-3:RAD.ARCH:15009

which, when clicked, is resolved by the NRS resolution server to the delivery URL:

   http://pds.lib.harvard.edu/pds/view/2573612

If in the future this resource is delivered through some other mechanism, the resolution server would be updated to resolve the persistent identifier to a new delivery URL; but the persistent identifier would remain unchanged and valid.