<https://brktn.com/2018/07/18/%e3%83%af%e3%82%a4%e3%83%a4%e3%83%ac%e3%82%b9%e3%82%a4%e3%83%a4%e3%83%9b%e3%83%b3-%e3%81%8a%e3%81%99%e3%81%99%e3%82%81/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://brktn.com/2018/07/18/%E3%83%AF%E3%82%A4%E3%83%A4%E3%83%AC%E3%82%B9%E3%82%A4%E3%83%A4%E3%83%9B%E3%83%B3-%E3%81%8A%E3%81%99%E3%81%99%E3%82%81/>