<https://kajitsu-soroban.com/archives/4199.html/%e4%bd%b3%e6%97%a5%e3%81%9d%e3%82%8d%e3%81%b0%e3%82%93%e9%80%9a%e4%bf%a1-vol-61>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://kajitsu-soroban.com/archives/4199.html/%E4%BD%B3%E6%97%A5%E3%81%9D%E3%82%8D%E3%81%B0%E3%82%93%E9%80%9A%E4%BF%A1-vol-61>