Harold Boley; Michael Kifer; Axel Polleres. <a href="http://www.w3.org/TR/2009/CR-rif-dtb-20091001/"><cite>RIF Datatypes and Built-Ins 1.0.</cite></a> 1 October 2009. W3C Candidate Recommendation. (Work in progress.) URL: <a href="http://www.w3.org/TR/2009/CR-rif-dtb-20091001/">http://www.w3.org/TR/2009/CR-rif-dtb-20091001/</a>