<http://www.w3.org/1999/02/22-rdf-syntax-ns#first>
<http://pop.h-cdn.co/assets/cm/15/06/54d0e835389cf_-_sheet_metal_08_0610-lg.jpg>
<http://www.popularmechanics.com/home/how-to-plans/how-to/a5940/how-to-work-with-sheet-metal/>