Making pretty diagrams with GraphViz

So recently I needed to draw some directed-graph diagrams - work-flow diagrams in this particular instance. After a bit of googling I came across some nice examples of diagrams produced by graphviz - actually what really turned me on to graphviz was this nice set of examples from Kent Bye.

A little tinkering and I soon had my workflow definitions (declared in xml in our application) rendered nicely with GraphViz. The markup language is deadly simple and intuitive, and the directed graphs - I didn't try anything else - which it produces are really good looking.

Lets take a look at some examples, starting simply with two nodes related in one direction only. The markup would look like this:

digraph {
  "Start" -> "End" [];
}

That's it.  No really.  This is all you need to create a simple, two-node directed graph diagram.  To draw the diagram you need to install graphviz (with a quality OS like ubuntu you just need the magic incantation "sudo apt-get install graphviz" and you're up and running. Once installed invoke graphviz like this:

dot -Tpng -oMyGraph.png MyGraph.dot

This invokes the directed-graph drawing tool, tells it to produce a png image from the input file "MyGraph.dot" and store it in the output file "MyGraph.png". The resulting diagram looks like this:

Coolness!

Lets get a bit trickier. We can control the size and shape of our nodes, and label the edges:

digraph {
  "A" [shape="circle"];
  "B" [shape="rectangle"];
  "C" [shape="diamond"];

  "A" -> "B" [label="A to B"];
  "B" -> "C" [label="B to C"];
  "A" -> "B" [label="A to C"];
}

Here's the diagram:

Isn't it just too cool? Last one coming up - this time with colours:

digraph {
  "Back" [shape="egg" color="green" style="filled" fillcolor="yellow"];
  "Forth" [shape="house" color="red"];
  "Other" [shape="invtriangle" color="blue"];

  "Back" -> "Forth" [color="orange" label="weee"];
  "Forth" -> "Back" [color="purple" label="eeew"];

  "Other" -> "Forth"
  "Other" -> "Back"
}

And here's how it looks:

I realize this just scratches the surface - there's a whole bunch of other node shapes you can use, you can define defaults for nodes and edges once at the beginning of your *.dot file, and much much more.

I only discovered GraphViz about 2 months ago, but since I did i've been using it quite a lot. Its very handy for drawing simple representations of work-flows, navigational flows, any kind of hierarchical structures (trees and graphs), etc., and just so simple to write. Generating the *.dot syntax programmatically is extremely easy - I now have our app invoking "dot" to generate the graphs on the fly.

Note: Google Charts now has experimental support for (a subset of) graphviz. Check it out here.You don't even have to install graphviz :)