<https://cutandperma.com/blog/%e3%83%a2%e3%83%a2%e3%83%b3%e3%83%a9%e3%82%a4%e3%83%96/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://cutandperma.com/blog/%E3%83%A2%E3%83%A2%E3%83%B3%E3%83%A9%E3%82%A4%E3%83%96/>