digraph OL {
    fontname=arial;
    node [fontname=arial, shape=box, style=filled, color=grey80];
    edge [fontname=arial, fontsize=12, dir=both];
    
    { rank=same; OL1; OL2 }
    { rank=same; IKC; PS }

    Stem;
    OL1 [ label="Object layer" ];
    OL2 [ label="Other object layer" ];

    subgraph cluster0 {
        bgcolor=grey90;
    
        A [label="Addressing" color=orange ];
        R [label="Routing", color=orange ];
        M [label="Monitoring", color=orange ];
        POE [ label="POE" ];
        POE -> Wheels;
        POE -> Selects;
        subgraph cluster2 {
            POE -> A [ label="Hooks", color=orange];
            POE -> R [ label="Hooks", color=orange];
            POE -> M [ label="Hooks", color=orange];
        }

    }

    POE2 [ label="Remote kernel"];

    PS [ label="Stem-compatibility"];

    OL2 -> POE;
    OL1 -> POE;
           POE -> IKC -> POE2;
           POE -> PS -> Stem;

}