Hi Damir,
In a recent copy of Moose, you can use Mondrian/Roassal to do similar visualizations. As an example of how you could create a similar output to the GraphViz for your example data, you could try the following code in a workspace:
|view class|
view := ROMondrianViewBuilder new.
class := { 'Car' -> 'tire1'. 'Car' -> 'tire2'. 'Car' -> 'tire3'. 'Car' -> 'tire4'. }.
class do: [:e| view shape circle withText node: e value].
view shape circle withText node: class first key.
view
edgesFromAssociations: class;
treeLayout.
view open
I am sure there are better ways to handle this, but this is roughly what I've been using myself. If you are working with class diagrams (or visualizing code), you should definitely look into importing the code into Moose itself, and utilizing its analysis tools - they are interesting and continue to evolve (and get more interesting).
-Chris