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A URN (also called a persistent identifier or name) is a persistent, location-independent identifier for a network-accessible resource. URNs generated from the HUL Name Resolution Service (NRS) look like this (urn-3:FHCL:12345) and are used like URLs (http://nrs.harvard.edu/urn-3:FHCL:12345). See the NRS section of this web site for more information.