<https://motani.jp/2007/07/09/%e5%8f%82%e8%ad%b0%e9%99%a2%e9%81%b8%e6%8c%99/#article>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://motani.jp/2007/07/09/%E5%8F%82%E8%AD%B0%E9%99%A2%E9%81%B8%E6%8C%99/>