<https://bbq-kyoto.com/blog/%e3%83%a9%e3%82%b9%e3%83%88%e3%82%bb%e3%83%bc%e3%83%ab%e5%ae%9f%e6%96%bd%e4%b8%ad/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://bbq-kyoto.com/blog/%E3%83%A9%E3%82%B9%E3%83%88%E3%82%BB%E3%83%BC%E3%83%AB%E5%AE%9F%E6%96%BD%E4%B8%AD/>