PURL

Persistent Uniform Resource Location

an interim measure - while Uniform Resource Names (URN-s) are being mainstreamed - to solve the problem of transitory URI-s in location-based URI schemes like HTTP.

does not directly describe the location of the resource to be retrieved but instead describes an intermediate (more persistent) location which, when retrieved, results in redirection (e.g. via a 302 HTTP status code) to the current location of the final resource.

http://en.wikipedia.org/wiki/Persistent_Uniform_Resource_Locator