<https://flow-style.com/2012/03/11/310%e3%83%9f%e3%82%b3%e3%83%8e%e3%82%b9%e3%83%bb%e3%82%b5%e3%83%97%e3%83%aa%e3%82%ab%e3%83%a9%e3%83%bc/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://flow-style.com/2012/03/11/310%E3%83%9F%E3%82%B3%E3%83%8E%E3%82%B9%E3%83%BB%E3%82%B5%E3%83%97%E3%83%AA%E3%82%AB%E3%83%A9%E3%83%BC/>