<https://www.totaro-r.com/information/r-performance/2017%e5%b9%b4%e9%80%9a%e5%b8%b8%e5%85%ac%e6%bc%94/357/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.totaro-r.com/information/r-performance/2017%E5%B9%B4%E9%80%9A%E5%B8%B8%E5%85%AC%E6%BC%94/357/>