<https://machida-petcl.com/blog/8%e6%9c%88%e3%81%ae%e3%82%aa%e3%83%9a%e5%ae%9f%e7%b8%be/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://machida-petcl.com/blog/8%E6%9C%88%E3%81%AE%E3%82%AA%E3%83%9A%E5%AE%9F%E7%B8%BE/>