<https://www.harunoryu.jp/blog/%e7%ab%8b%e5%86%ac%ef%bc%81%e4%bb%8a%e9%80%b1%e3%81%8b%e3%82%89%e3%81%90%e3%81%a3%e3%81%a8%e5%86%b7%e3%81%88%e3%82%8b/#article>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.harunoryu.jp/blog/%E7%AB%8B%E5%86%AC%EF%BC%81%E4%BB%8A%E9%80%B1%E3%81%8B%E3%82%89%E3%81%90%E3%81%A3%E3%81%A8%E5%86%B7%E3%81%88%E3%82%8B/>