L. Daigle, D. van Gulik, R. Iannella, P. Faltstrom. <a href="http://www.ietf.org/rfc/rfc3406.txt"><cite> URN Namespace Definition Mechanisms.</cite></a>. IETF RFC 3406 October 2002. URL: <a href="http://www.ietf.org/rfc/rfc3406.txt"> http://www.ietf.org/rfc/rfc3406.txt</a>