GraphViz enforce columns - graphviz

Question

I have the following dot:
digraph G
{
rank="same";
subgraph sys
{
1 [shape=record, label="| | Système"];
}
subgraph obj
{
2 [shape=box, label="Sites"];
3 [shape=box, label="Sociétés de\nmaintenance"];
1 -> 2 [arrowhead=none] [label="a"];
1 -> 3 [arrowhead=none] [label="b"];
}
subgraph constraints
{
4 [style=dotted, label="Surveiller"];
5 [style=dotted, label="Effectuer des\ninterventions"];
4 -> 2 [style=dotted];
4 -> 3 [style=dotted];
5 -> 2 [style=dotted];
5 -> 3 [style=dotted];
}
}
Which gives me this image:
But I want to have a subgraph by column (1 on the first column, 2-3 on the second and 4-5 on the last).
Is there a way to do that?
For your help,
Thanks by advance.

Answer 1

digraph G
{
rank=same
rankdir=LR
subgraph sys
{
1 [shape=record, label="| | Système"]
}
subgraph obj
{
node [shape=box]
2 [label="Sites"]
3 [label="Sociétés de\nmaintenance"]
}
subgraph constraints
{
node [style=dotted]
4 [label="Surveiller"]
5 [label="Effectuer des\ninterventions"]
}
edge [style=invis, weight=2]
2->4
3->5
edge [style=dotted]
4 -> 2
4 -> 3
5 -> 2
5 -> 3
edge [style="" arrowhead=none]
1 -> 2 [label="a"]
1 -> 3 [label="b"]
}
This solution is the same as suggested by #alexandr_anturis (+1), but I have removed some irrelevant 'syntax noise', because I feel that such a complex and powerful specification as dot language benefits of any simplification available.
Use rankdir and hidden edges with appropriate weight.
Picture of the result:

Answer 2

digraph G
{
rank="same";
layout="dot";
rankdir=LR;
subgraph sys
{
style=filled;
1 [rank=1, shape=record, label="| | Système"];
}
subgraph obj
{
2 [rank=2,shape=box, label="Sites"];
3 [rank=3,shape=box, label="Sociétés de\nmaintenance"];
}
subgraph constraints
{
4 [rank=4,style=dotted, label="Surveiller"];
5 [rank=5,style=dotted, label="Effectuer des\ninterventions"];
}
2->3->4->5 [color=white, weight=100];
rankdir=LR;
4 ->2 [style=dotted, w=0];
4 -> 3 [style=dotted, w=0];
5 -> 2 [style=dotted, w=0];
5 -> 3 [style=dotted, w=0];
1 -> 2 [arrowhead=none] [label="a"];
1 -> 3 [arrowhead=none] [label="b"];
}
You can use something like this. The way to make what you want is to use rankdir and add invisible edges for correct ranking.