digraph graph_03
{
graph [ label="Cluster set" rankdir="TB" ]

subgraph "cluster A"
{
graph [ label="Cluster A" rankdir="TB" ]

"A" [ color="blue" ]
"B" [ color="blue" ]
"A" -> "B" [ color="green" label="" ]
}

subgraph "cluster C"
{
graph [ label="Cluster C" rankdir="TB" ]

"C" [ color="blue" ]
"D" [ color="blue" ]
"C" -> "D" [ color="red" label="" ]
}
}
