Natasha Noy. <a href="http://www.w3.org/TR/2005/NOTE-swbp-classes-as-values-20050405"><cite>Representing Classes As Property Values on the Semantic Web.</cite></a> 5 April 2005. W3C Note. URL: <a href="http://www.w3.org/TR/2005/NOTE-swbp-classes-as-values-20050405">http://www.w3.org/TR/2005/NOTE-swbp-classes-as-values-20050405</a>