Onion graphs: aesthetics and layout

In many engineering disciplines it is interesting to use diagrams which combine a graph notation with an onion notation. It is observed that such onion graphs lend themselves easily to some kinds of sophisticated tool support, but also that the need for tool support is significantly larger than for ordinary graphs. Most notably there is a need for supporting automatic layout to a much larger extent than for traditional graphs, particularly of the incremental kind. Some aesthetics and algorithms are outlined for the layout of onion graphs