// dot -Tpng refs_types.dot > refs_types.png
digraph {
  Papers[label="Papers\n(fatcat; incl. datasets)",shape=rect]
  Books[label="Books\n(openlibrary)",shape=rect]
  Encyclopedia[label="Encyclopedia\n(wikipedia, [en])",shape=rect]
  Web[label="Web\n(wayback machine)",shape=rect]
  // OtherMedia[label="Other Media? TODO\n(archive.org)", color=orange]
  Unmatched[label="Unknown/Unmatched", color=grey]
  Papers -> Papers[color=green,label="1.3 billion",penwidth=2]
  Papers -> Unmatched[color=orange,label="0.7 billion (wip)",penwidth=2]
  Papers -> Books[color=green,label="20 million"]
  Papers -> Web[color=orange,label="25 million (wip)"]
  // Books -> Papers[color=red]
  // Books -> Web[color=red]
  // Books -> Books[color=red]
  Encyclopedia -> Papers[color=green,label="1.3 million"]
  // Encyclopedia -> Books[color=gray,label="TODO"]
}