M. Mealling. <a href="http://www.ietf.org/rfc/rfc3061.txt"><cite>A URN Namespace of Object Identifiers. </cite></a>. IETF RFC 3061. February 2001. URL: <a href="http://www.ietf.org/rfc/rfc3061.txt">http://www.ietf.org/rfc/rfc3061.txt</a>