Editing Persistent uniform resource locator (section)

{{Short description|OCLC-designed persistent identifier scheme}}
{{redirect|PURL|other meanings of "purl"|Purl (disambiguation)}}

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 [[URL redirection|redirect]] to the location of the requested [[web resource]]. PURLs redirect [[HTTP]] clients using [[List of HTTP status codes|HTTP status codes]]. 

Originally, PURLs were recognizable for being hosted at '''purl.org''' or other hostnames containing <code>purl</code>. Early on many of those other hosts used descendants of the original OCLC PURL system software. Eventually, however, the ''PURL concept'' came to be generic and was used to designate any redirection service (named ''PURL resolver'') that:<ref>Services as [[Lex (URN)|URN LEX]], [[European Legislation Identifier|ELI]] and [[Digital object identifier|DOI]], [[Permalink]] and others, they use directly or indirectly the PURL concept.</ref>  
* has a "root URL" as the ''resolver'' reference (e.g. <code><nowiki>http://myPurlResolver.example</nowiki></code>);
* provides means, to its user-community, to include new ''names'' in the root URL (e.g. <code><nowiki>http://myPurlResolver.example/name22</nowiki></code>);
* provides means to associate each ''name'' with its URL (to be redirected), and to update this redirection-URL;
* ensure the persistence (e.g. by contract) of the root URL and the ''PURL resolver'' services.
  
PURLs are used to curate the URL resolution process, thus solving the problem of transitory URIs in location-based [[URI scheme]]s like HTTP. Technically the ''string resolution'' on PURL is like ''[[SEF URL]] resolution''.
The remainder of this article is about the OCLC's PURL system, proposed and implemented by [[OCLC]] (the Online Computer Library Center).