Thanks, Steve for your interest in my question.
The example attached at the java venn diagram link you sent is closest to what I had in mind.
Closer still would be to imagine either of the two halves of the image with an optional V in the intersection of X and Z and an optional XZ label for the union of X and Z and an optional XYZ label for the union of those three categories. I say “optional” because there are times when the unions and intersections have names and other times when that’s not important. With more complicated labeling colors or arrows would probably be needed to associate labels with their sets.
The set relationships are independent of the way they are displayed. Most of the flow diagrams I see in the Graphviz gallery could be illustrated with set diagrams like the one attached, and vice versa.
