! The above image was drawn in http://magjac.com/graphviz-visual-editor/ using the following code:
graph ER {
fontname="Helvetica,Arial,sans-serif"
node [fontname="Helvetica,Arial,sans-serif"]
edge [fontname="Helvetica,Arial,sans-serif"]
layout=neato
node [shape=box]; theme1; "theme 2"; theme3;
node [shape=ellipse]; resource1; "resource 2"; "resource 3"; "resource 4";
theme1 -- resource1;
theme1 -- "resource 2";
theme3 -- "resource 2";
theme1 -- "resource 3";
"theme 2" -- "resource 2";
"theme 2" -- "resource 4";
theme3 -- resource1;
theme3 -- "resource 4";
label = "\n\nEntity Relation Diagram\ndrawn by NEATO";
fontsize=20;
} ```