<https://secure.gravatar.com/avatar/c113390cdea3ebaef835a59ad8f01f51?s=96&amp;d=mm&amp;r=g>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.kennethkwok.me/blog/2016/02/12/%E5%A4%A7%E8%BC%B8%E5%AE%B6/>