<https://tsukuba-daigaku.com/blog/%e3%82%bb%e3%83%ac%e3%82%af%e3%83%88%e2%85%a3%e3%81%ae%e3%81%8a%e9%83%a8%e5%b1%8b%e5%8f%a3%e3%82%b3%e3%83%9f-%e7%a4%be%e5%b7%a5>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://tsukuba-daigaku.com/blog/%E3%82%BB%E3%83%AC%E3%82%AF%E3%83%88%E2%85%A3%E3%81%AE%E3%81%8A%E9%83%A8%E5%B1%8B%E5%8F%A3%E3%82%B3%E3%83%9F-%E7%A4%BE%E5%B7%A5>