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A persistent uniform resource locator (PURL) is a Uniform Resource Locator (URL) (i.e. location-based Uniform Resource Identifier or URI) that is used to redirect to the location of the requested Web resource. PURLs redirect HTTP clients using HTTP status codes. PURLs are used to curate the URL resolution process, thus solving the problem of transitory URIs in location-based URI schemes like HTTP. Technically the string resolution on PURL is like SEF URL resolution. (Excerpt from <a href="http://en.wikipedia.org/wiki/Persistent_Uniform_Resource_Locator">Wikipedia article: PURL</a>)