<https://forum.vanhoctre.com/threads/ban-ve-van-e-o-nhiem-moi-truong.13237/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://forum.vanhoctre.com/threads/ban-ve-van-e-o-nhiem-moi-truong.13237/>