Deborah L. McGuinness; Michael K. Smith; Chris Welty. <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210"><cite>OWL Web Ontology Language Guide.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210">http://www.w3.org/TR/2004/REC-owl-guide-20040210</a>