<https://www.ota-estate.net/blog/topics/%e3%83%91%e3%83%bc%e3%82%af%e3%82%b5%e3%82%a4%e3%83%89%e6%b4%97%e8%b6%b3%e6%b1%a0%e5%a3%b2%e5%8d%b4%e6%9f%bb%e5%ae%9a/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.ota-estate.net/blog/topics/%E3%83%91%E3%83%BC%E3%82%AF%E3%82%B5%E3%82%A4%E3%83%89%E6%B4%97%E8%B6%B3%E6%B1%A0%E5%A3%B2%E5%8D%B4%E6%9F%BB%E5%AE%9A/>