<http://www.w3.org/1999/02/22-rdf-syntax-ns#first>
<http://pop.h-cdn.co/assets/cm/15/13/640x320/54cb2acf096b4_-_sapwood-filter-0214-de.jpg>
<http://www.popularmechanics.com/science/environment/a10143/a-simple-tree-branch-can-become-a-backyard-water-filter-16540288/?click=pm_latest>