DOT Graphs

DOT (filename.dot) is a file format to draw graphs including directed graphs.
DOT writes graphs in .ps, .pdf, .gif, .png formats.

For example,

$ dot -Tps src.dot -o dest.ps

$ dot -Tpdf src.dot -o dest.pdf

Dot file  format is as follows:

digraph graphName {
 "Node 1"  -> "Node 2"  ;
 "Node 1" -> "Node 2" -> "Node 3";
}

Each line is terminated by semicolon (;), and arrow (->) is used to show directed arc.

digraph means directed graph whereas graph means undirected graph.

Within a main graph a subgraph define a subset of graph.
For example,
digraph GraphName {
"Node 1" -> "Node 2";
 subgraph SubGraphName{
   "Node 3" -> "Node 1";
   "Node 4" -> Node 3";
  }
}