use Graph::Easy;
my $graph = Graph::Easy->new();
my @nodes=('b:a','c:a','d:b','e:c','f:c');
my ($child,$parent);

# build the graph
foreach my $node (@nodes) {
        ($child,$parent) = split(":",$node);
        $graph->add_edge($parent,$child);
}

# print the graph
print $graph->as_asciii();

##</code><code>##

# save the graph by saving the list of original nodes
open($filehandle,"<","nodes.dat") or die("Can't open file 'nodes.dat' for writing: $!\n");
print $filehandle join("\n",@nodes);