<https://www.egingpoint.com/posts/18%e5%b9%b4%e5%8f%b0%e9%a2%a821%e5%8f%b7%e3%81%ae%e5%bd%b1%e9%9f%bf.html/20190608_002/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.egingpoint.com/posts/18%E5%B9%B4%E5%8F%B0%E9%A2%A821%E5%8F%B7%E3%81%AE%E5%BD%B1%E9%9F%BF.html/20190608_002/>