<https://musashi.silk.to/blog/2007/06/08/%e3%83%9c%e3%82%af%e3%81%ae%e3%81%8a%e3%82%82%e3%81%a1%e3%82%83/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://musashi.silk.to/blog/2007/06/08/%E3%83%9C%E3%82%AF%E3%81%AE%E3%81%8A%E3%82%82%E3%81%A1%E3%82%83/?replytocom=986>