This example is adapted from https://graphviz.org/content/cluster.
USING: graphviz graphviz.notation graphviz.render ;
<digraph>
"dot" =layout
0 <cluster>
"filled" =style
"lightgrey" =color
[node "filled" =style "white" =color ];
{ "a0" "a1" "a2" "a3" } ~->
"process #1" =label
add
1 <cluster>
[node "filled" =style ];
{ "b0" "b1" "b2" "b3" } ~->
"process #2" =label
"blue" =color
add
"start" "a0" ->
"start" "b0" ->
"a1" "b3" ->
"b2" "a3" ->
"a3" "a0" ->
"a3" "end" ->
"b3" "end" ->
"start" [add-node "Mdiamond" =shape ];
"end" [add-node "Msquare" =shape ];
preview