<https://niiji.com/blog/%e4%ba%a4%e9%80%9a%e4%ba%8b%e6%95%85%e6%b2%bb%e7%99%82%e3%81%ae%e3%81%94%e7%9b%b8%e8%ab%87/#article>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://niiji.com/blog/%E4%BA%A4%E9%80%9A%E4%BA%8B%E6%95%85%E6%B2%BB%E7%99%82%E3%81%AE%E3%81%94%E7%9B%B8%E8%AB%87/>