The rules proposed for creating easily legible diagrams determine mathematical limits for the proposed visual language. (Prime example: no crossing of arrows.)
I tried to do this with a JS library: http://glench.github.io/fuzzyset.js/ui/
It looks like since this paper the author(s?) have developed it further and built some real stuff. Here's a screenshot on their website: http://drakon-editor.sourceforge.net/folder-parrot.png
Is this an easier representation to read and understand? I'm not so sure.