<https://perl.no-tubo.net/2008/09/25/mysql%e3%81%ae%e8%a4%87%e5%90%88%e3%82%a4%e3%83%b3%e3%83%87%e3%83%83%e3%82%af%e3%82%b9%e6%b3%a8%e6%84%8f%e7%82%b9/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://perl.no-tubo.net/2008/09/25/mysql%E3%81%AE%E8%A4%87%E5%90%88%E3%82%A4%E3%83%B3%E3%83%87%E3%83%83%E3%82%AF%E3%82%B9%E6%B3%A8%E6%84%8F%E7%82%B9/>