graphviz/subgraph_uml.dot

digraph {
  subgraph cluster_house {
    label="House"
    hcw [label="Clean water"]
    hdw [label="Dirty water"]
  }
  subgraph cluster_street {
    label="Street"
    scw [label="Clean water"]
    sdw [label="Dirty water"]
  }
  scw -> hcw
  hdw -> sdw
}