<https://takeichimusic.com/blog/%e6%bc%94%e5%a5%8f%e3%81%af%e3%83%9e%e3%83%a9%e3%82%bd%e3%83%b3%ef%bc%9f/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://takeichimusic.com/blog/%E6%BC%94%E5%A5%8F%E3%81%AF%E3%83%9E%E3%83%A9%E3%82%BD%E3%83%B3%EF%BC%9F/>