Problems with designing UML - like diagrams in graphviz - graphviz

Question

I'm currently having issues with designing UML-like diagrams on graphiz. The reason for the problem is that they are not exactly UML diagrams. The main difference is that I make use of indentations to add an hierarchy to an object's properties. Implementing these idiosyncrasies is a little difficult for me. What I'm trying to achieve is this:
I normally use a node shape called record to design these diagrams. The problem arises when I have to link two of these UML-like diagrams just like relationships in UML i.e. aggregation, association, composition, etc.
When I have the diagrams, I can't make the relationship with the arrows because the arrows only go from a random part of one node to another random part of the other node.
The way I have the UML-like diagrams is good, but the relationship arrow causes it not to be what I want as I want the arrows to go from a specific point of one node to another specific point of another node.
The DOT code I used to create this graph is like this:
digraph G {
fontname = "Bitstream Vera Sans"
fontsize = 8
node [
fontname = "Bitstream Vera Sans"
fontsize = 8
shape = "record"
]
edge [
fontname = "Bitstream Vera Sans"
fontsize = 8
]
Person [
label = "{Person \l\l \ age : int\l \ livesIn : City \l \ \ \ sinceYear : int}"
] // \l -new line, \ -indentation
City [
label = "{City \l \ \ name : string}"
]
Person -> City
}
I tried getting around this problem by using horizontal line divisions within the nodes even though I didn't want the lines. The horizontal line divisions make it possible for me to make this specific relationship possible by using ports, but they create a new problem of their own. The problem they create is that they get rid of the indentations I want and had in the previous graph. The way I tried to get around the arrow problems works, but new problems are created - the indentation disappears and the horizontal line divisions can't be made invisible
.
The code I used to create this graph is:
digraph G {
fontname = "Bitstream Vera Sans"
fontsize = 8
node [
fontname = "Bitstream Vera Sans"
fontsize = 8
shape = "record"
penwidth = 0.5
]
edge [
fontname = "Bitstream Vera Sans"
fontsize = 8
]
Person [
label = "{<g0> Person | <g1> age : int | <g2> livesIn : City | <g3> sinceYear : int}"
] // \l -new line, \ -indentation
City [
label = "{<f0> City | <f1> name : string}"
]
Person:<g2> -> City:<f1> [arrowhead = "empty", headlabel = "*"]
}
These indentations are a big part of the relationship, so I'm wondering if anyone knows what I can do to have these indentations back in the diagrams as well what I can do to make the horizontal line divisions invisible?
I'll appreciate if someone has a better way/idea that's also totally different from what I have done in diagrams 2 & 3, that will help me achieve diagram 1.

Answer 1

Your original attempt wasn't bad. I would say using ports is definitely the way to go.
If you place the node in a cluster you can use the cluster's border and hide the border of the record node, getting rid of those divider lines.
As you noted, using a backslash \ no longer works to escape a space. The workaround is to either use \ instead, this will escape the whitespace. As an alternative you could also replace each space with an &nnbsp;. Either one will achieve the required effect.
I made some minor changes to make things more readable, like put Graph properties in a graph block instead of in the root of the graph and rename the port-names to something more sensible. I also removed any ports not in use.
The final result I came up with was this:
...and this is the DOT code I used:
digraph G {
graph [
compound = true // To clip the head at the cluster border
penwidth = 2 // Make the cluster's borders a bit thicker
rankdir = "LR" // Make the arrow and nodes go from Left to Right
ranksep = 1 // Add a bit more space inbetween nodes
]
node [
color = none // Hide the node's border
fontname = "Bitstream Vera Sans"
height = 0 // Make the node as small as possible (it will grow if it needs more space)
margin = 0 // Remove unneeded whitespace
shape = "record" // So we can use ports
]
edge [
arrowhead = "open"
labelangle = -5 // Place the asteriks closer to the line
labeldistance = 2.5 // Place the asteriks further away from the arrow head
penwidth = 2 // Make the line a bit thicker
]
/* #NOTE: escaping spaces in the label using '\' doesn't work so use '&nbsp' or '&#92' instead. */
subgraph cluster_Person {
Person [
label = "\N\l | \ \ \ age : int\l | <livesIn> \ \ \ livesIn : City\l | \ \ \ \ \ \ sinceYear : int\l"
]
}
subgraph cluster_City {
City [
label = "<city> \N\l | \ \ \ name : string\l"
]
}
Person:livesIn -> City:city [headlabel = "*", lhead = "cluster_City"] // lhead allows us to point to the cluster's border instead of the node, as long as we add `compound = true` to the graph
}