<https://kyokokonno.net/2015/07/05/%e6%b2%bc%e6%b4%a5%e3%81%b8%ef%bc%81/#article>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://kyokokonno.net/2015/07/05/%E6%B2%BC%E6%B4%A5%E3%81%B8%EF%BC%81/>