<http://www.reddit.com/r/webdev/comments/2gypch/is_schemaorg_still_a_thing/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://forum.edugorilla.com/forums/topic/the-value-of-ultimate-period-of-oscillation-pu-is-3-min-and-that-of-the-ultimate-controller-gain-kc/>