<https://tsukuba-daigaku.com/blog/%e3%80%90%e7%b4%b9%e4%bb%8b%e3%80%91%e4%b8%80%e8%aa%a0%e5%95%86%e4%ba%8b%e6%a0%aa%e5%bc%8f%e4%bc%9a%e7%a4%be>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://tsukuba-daigaku.com/blog/%E3%80%90%E7%B4%B9%E4%BB%8B%E3%80%91%E4%B8%80%E8%AA%A0%E5%95%86%E4%BA%8B%E6%A0%AA%E5%BC%8F%E4%BC%9A%E7%A4%BE>