<https://satoshi-kimura.net/blog/%e3%83%88%e3%83%ac%e3%83%bc%e3%83%8b%e3%83%b3%e3%82%b0/post-2356#primaryimage>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://satoshi-kimura.net/blog/%E3%83%88%E3%83%AC%E3%83%BC%E3%83%8B%E3%83%B3%E3%82%B0/post-2356>