<https://blog.aerobile.com/category/%e5%87%ba%e5%9c%8b%e4%b8%8a%e7%b6%b2%e7%9c%8b%e9%80%99%e8%a3%a1/%e6%97%a5%e6%9c%ac%e4%b8%8a%e7%b6%b2/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://blog.aerobile.com/japan-internet-study/>