Priscilla Walmsley; Ashok Malhotra; Charles Campbell. <a href="http://www.w3.org/TR/2003/WD-xmlschema-11-req-20030121"><cite>Requirements for XML Schema 1.1.</cite></a> 21 January 2003. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2003/WD-xmlschema-11-req-20030121">http://www.w3.org/TR/2003/WD-xmlschema-11-req-20030121</a>