use Graph::Directed;

my $g = Graph::Directed->new();

# Each pair is a pair of vertices qw|a b| indicating 
# a directed edge from a to b
# graph: lineitem <-> invioce <-> claim <-> insurer
$g->add_edges( qw| lineitem invoice  invoice lineitem
                   invoice claim  insurer claim
                   claim invoice  claim insurer|);

print "Strongly connected components: ", $g->strongly_connected_graph, "\n";