Horizontally partitioning nodes in a graph - graphviz

Question

I'm using the dot command to generate a graph of, in this case, a series of software releases, showing the relationship among the releases.
Assumptions:
Each release has a number, with higher numbers denoting later releases.
Each release must appear above earlier releases in the graph.
Each release is based on a specific earlier release, not necessarily the most recent one.
Each "based-on" relationship is shown as an arrow from one node to another.
Some subset of the releases are separate, for reasons that aren't important to the question. I'll call them "alt" releases. "Alt" releases can be based on non-"alt" releases, and vice versa. (It happens that I'm more interested in the non-"alt" releases, but I want all releases in the graph.)
I can generate a graph that clearly shows the relationships among the releases, but I also want to put all the "alt" releases on the right side of the vertical graph, and all the non-"alt" releases on the left side -- while maintaining all the relationship information (which means arrows going from the left side of the graph to the right, and vice versa).
I've tried putting the "alt" nodes into a subgraph/cluster, but that loses the dependencies (arrows) between nodes in the cluster and nodes outside it.
I've also tried creating an invisible node in the "middle" and defining dependencies from every node to the "middle" node while specifying the direction, but I was unable to mix vertical and horizontal dependencies in the same graph.
Here's the demo.dot file I have so far, which does not do the partitioning I want:
digraph releases {
// Use a box shape for all nodes
node [shape=box];
// Define labels for nodes
v106 [style=bold];
v105 [label="v105 alt" style=dashed];
v104;
v103;
v102 [label="v102 alt" style=dashed];
v101 [style=bold];
// Define dependencies
v106 -> v104;
v106 -> v105 [style=dashed];
v105 -> v102;
v104 -> v101;
v103 -> v101;
v102 -> v101;
// Use [style=invisible dir=none] to ensure that a later node appears above
// an earlier one even if there's no dependency.
v106 -> v105 [style=invisible dir=none];
v105 -> v104 [style=invisible dir=none];
v104 -> v103 [style=invisible dir=none];
v103 -> v102 [style=invisible dir=none];
v102 -> v101 [style=invisible dir=none];
}
And here's the image file, generated with dot -Tpng demo.dot -o demo.png
What I want is to have all the "alt" nodes to the right of an invisible vertical line and all the other nodes to the left of it, with all the arrows still in place (distorted as necessary).
Is there a way to do this with dot? Or is there another tool (usable on Linux, specifically Debian) that can do the same thing?

Answer 1

This is a very late answer but may help others.
Graphviz tries to keep edges straight if both nodes belog to the same group.
digraph releases { nodesep=0.5
// Use a box shape for all nodes
node [shape=box];
// Define regular nodes
{
node [group=regular];
v106 [style=bold];
v104;
v103;
v101 [style=bold];
}
// Define alt nodes
{
node [group=alt style=dashed];
v102 [label="v102 alt"];
v105 [label="v105 alt"];
}
// Define dependencies
v106 -> v104;
v106 -> v105 [style=dashed];
v105 -> v102;
v104 -> v101;
v103 -> v101;
v102 -> v101;
// Use [style=invisible dir=none] to ensure that a later node appears above
// an earlier one even if there's no dependency.
edge [style=invisible dir=none];
v106 -> v105;
v105 -> v104;
v104 -> v103;
v103 -> v102;
v102 -> v101;
}
gives

Answer 2

Trying to do something similar. Adding this to your code gets close:
subgraph cluster_alt {
graph [style= invisible];
edge [style = invisible, arrowhead=none];
weight = 10;
v102 -> v105;
}
subgraph cluster_main {
graph [style= invisible];
edge [style = invisible, arrowhead=none];
weight = 10;
v106 -> v105-> v104->v103->v102->v101;
}
Gives me:
The "weight" attribute pushes the edges in these invisible subgraphs towards being more vertical than the other edges (the visible ones you've already defined).