How can I create named edge “types” in Graphviz/dot/neato?

Question

I need to draw a diagram with graphviz/dot where there are common edge types between nodes and am trying to find a way to define a label for each type of edge and then use t

Answer 1

Not really an answer but "food for thought" as I don't think named labels exist in graphviz: You could define a default label for the following edges. That works well if your workflow allows to define edges all in one place. Example:

digraph rs
{
    node[ shape = box, style = rounded]

    edge[ label = "pull" ];
    { A B } -> C;
    G -> H;
    C -> D[ label = "stop" ];
    edge[ label = "push"];
    D -> { E F };
    edge[ color = red, fontcolor = red ];
    { E F } -> G;
}

which yields

I have also tried to implement your diagramm with

digraph fan 
{
    splines = ortho;
    node [ shape=box ]

    edge [ xlabel = "Pull", minlen = 4 ];
    { rank = same; OFF  -> HIGH -> LOW; }
    LOW:s -> OFF:s;
}

which produces

so it looks good but with all the tweaking is difficult to expand.

Answer 2

I think I got your solution, using m4 (thanks to Simon). Using and adapting your sample, I created a file called gv.m4:

digraph {
    define(`edge_x',`[label="type x", color=red, style=solid]')
    define(`edge_y',`[label="type y", color=green, style=dashed]')
    define(`edge_z',`[label="type z", color=blue, style=dotted]')

    subgraph cluster_1 {
        a -> b edge_x;
        b -> a edge_y;

        b -> c edge_x;
        c -> b edge_y;

        c -> d edge_z;
    }

    subgraph cluster_2 {
        d -> e edge_x;
        e -> d edge_y;

        e -> f edge_x;
        f -> e edge_y;

        f -> c edge_z;
    }
}

and converted it with the simple command

m4 gv.m4 > gv.dot

which now contains your defined edges

digraph {

    subgraph cluster_1 {
        a -> b [label="type x", color=red, style=solid];
        b -> a [label="type y", color=green, style=dashed];

        b -> c [label="type x", color=red, style=solid];
        c -> b [label="type y", color=green, style=dashed];

        c -> d [label="type z", color=blue, style=dotted];
    }

    subgraph cluster_2 {
        d -> e [label="type x", color=red, style=solid];
        e -> d [label="type y", color=green, style=dashed];

        e -> f [label="type x", color=red, style=solid];
        f -> e [label="type y", color=green, style=dashed];

        f -> c [label="type z", color=blue, style=dotted];
    }
}

and yields the expected graph:

You can do much more with m4 - stuff that is missing in graphViz, like maintaining and (even conditionally) including subfiles. For example, if you put your two subgraphs into two separate files gv1.txt and gv2.txt, this would work nicely:

digraph incl
{
    define(`edge_x',`[label="type x", color=red, style=solid]')
    define(`edge_y',`[label="type y", color=green, style=dashed]')
    define(`edge_z',`[label="type z", color=blue, style=dotted]')
    include(gv1.txt)
    include(gv2.txt)
     e -> d[ color = yellow, label = "this is new!"];
}