<https://eglantyne2.net/blog/2011/05/%e9%9b%a8%e3%81%a7%e3%81%99%e3%81%ad%ef%bd%9e%e3%80%82/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://eglantyne2.net/blog/2011/05/%E9%9B%A8%E3%81%A7%E3%81%99%E3%81%AD%EF%BD%9E%E3%80%82/>