Overlapping ranks - Creating a block diagram - block

Question

I nearly spent the whole day trying to get a block diagram out of Graphviz. The biggest problem seems to be that I've got vertical as well as horizontal ranking. Easier shown than explained, so here is how the diagram should look:
This is my Dot-Code so far:
digraph block_diagram
{
graph [ splines=ortho, rankdir=TB];
node [shape=box, style=filled, fontname=Arial];
layer_0 [style="rounded,filled", fillcolor="#99ccff", width=15, height=1, label="Layer 0"];
layer_1 [shape=box, width=5, height=1, label="Layer 1"];
//emptybox [shape=box,height=1, label=""];
layer_1_1 [shape=box, width=5, height=1, label="Layer 1_1"];
layer_2 [shape=box, width=5, height=1, label="Layer 2"];
layer_3 [shape=box, width=5, height=1, label="Layer 3"];
layer_4 [shape=box, width=5, height=1, label="Layer 4"];
application [shape=box, width=3, height=5, label="Application"];
layer_0 -> { layer_1 application };
layer_0 -> layer_1 -> layer_1_1 -> layer_2 -> layer_3 -> layer_4;
application -> { layer_2 layer_3 layer_4 };
}
It looks like this -
I tried to group the nodes and rank them, but in the end all have the same rank and the diagram just looks wrong.
I don't know what to do anymore, and I hope someone can help me.
P.S.: I also don't know to create a shape like 'Layer 1'

Answer 1

Summary: This answer presents a variant using auxiliary nodes, still looking for a variant with no extra nodes and clusters.
If you create several invisible nodes within a cluster, you can get desired visual behavior, as in this image:
This is possible through the use of the attribute newrank=true to graph and { rank=same; nodename1; nodename2; ... } for horizontal alignment desired nodes. To hide auxiliary nodes, you need to give them an attribute style=invis, to hide cluster's borders add attribute color=none to cluster.
For vertical alignment, group the desired nodes by giving them an attribute group=g1, here g1 is your custom name for column of nodes.
Layer 1 and Layer 1_1 nodes can be created as table cells.
Bi-directional edges created with dir=both.
To make the line end at the cluster boundary, I used attribute compound=true for graph and lhead, ltail for edge.
Final image:
Script:
digraph block_diagram {
graph [
newrank=true,
ranksep=0,
nodesep=0,
splines=ortho,
compound=true,
fontname="Arial" ];
node [
shape=box,
style=filled,
fontname="Arial",
fontsize=14 ];
subgraph cluster_0{
fillcolor="#99ccff"
style="rounded, filled"
layer_0 [
label=<<B>Layer 0</B>>,
fillcolor=none,
shape=none
width=1 ];
a1 [group=g1 width=1.5 style=invis]
a2 [group=g2 width=1.5 style=invis]
}
subgraph cluster_1_1 {
color=none;
layer_1 [
group=g1,
fillcolor=none,
shape=none,
margin=0,
label= <<table border="0" cellspacing="0" cellborder="1">
<tr>
<td width="40" height="30" fixedsize="true" BGCOLOR="#ccffff" sides="TL"></td>
<td width="80" height="30" fixedsize="true" BGCOLOR="#ccffff" sides="TRB" ALIGN="LEFT"><B>Layer 1</B></td>
</tr>
<tr>
<td width="40" height="30" fixedsize="true" BGCOLOR="#ccffff" sides="RBL"></td>
<td COLSPAN="2" width="72" height="26" fixedsize="true" BGCOLOR="#ccffff" sides="TBRL" VALIGN="BOTTOM"><B>Layer 1_1</B></td>
</tr></table>>]
layer_2 [
group=g1,
label=<<B>Layer 2</B>>,
fillcolor ="#ccffff",
width=1.6 ];
}
layer_underline [
group=g1,
label="",
margin=0;
shape=underline,
fillcolor=none,
width=2,
height=0 ];
subgraph cluster_1_2{
color=none;
layer_3 [
group=g1,
label=<<B>Layer 3</B>>,
fillcolor="#ccff99",
width=1.6 ];
layer_4 [
group=g1,
label=<<B>Layer 4</B>>,
fillcolor="#ccff99",
width=1.6 ];
}
subgraph cluster_2 {
style=filled;
fillcolor="#dde6ed"
b1 [group=g2 style=invis]
application [
group=g2,
label=<<B>Application</B>>,
shape=none
fillcolor=none
width=2 ];
b2 [group=g2 style=invis]
}
a1 -> layer_0 [style=invis]
layer_0 -> a2 [style=invis]
a1 -> layer_1 [minlen=3 ltail="cluster_0" lhead="cluster_1_1" dir="both" color="#99ccff" penwidth=5 arrowsize=.5]
a2 -> b1 [ltail="cluster_0" lhead="cluster_2" dir=both color="#99ccff" penwidth=5 arrowsize=.5]
layer_1 -> layer_2 [style=invis];
layer_2 -> layer_underline [ color="#99ccff" penwidth=5 arrowsize=.5 dir=back ltail="cluster_1_1"]
layer_underline -> layer_3 [ color="#99ccff" penwidth=5 arrowsize=.5 lhead="cluster_1_2"]
layer_3 -> layer_4 [style=invis]
b1 -> application [style=invis]
application -> b2 [style=invis]
layer_4 -> b2 [color="#99ccff" penwidth=5 arrowsize=.5 ltail="cluster_1_2" lhead="cluster_2" dir=both]
layer_2 -> application [color="#99ccff" penwidth=5 arrowsize=.5 ltail="cluster_1_1" lhead="cluster_2" dir=both]
{ rank=same; layer_4; b2 }
{ rank=same; layer_1; b1 }
{ rank=same; layer_underline; application }
{ rank=same; a1; layer_0; a2 }
}