CREATE TABLE node (node_id, <bunch of other node related columns>);
CREATE TABLE edge (edge_id, from_node_id, to_node_id, <bunch of other edge related columns>);

##</code><code>##

sub _edges {
  my (%args) = @_;
  
  my $node_id = $args{node_id};
  my $limit   = $args{limit} || 1;
  my $edges   = $args{edges} || [];
  my $iter    = $args{iter}  || 1;
  my $seen    = $args{seen}  || [];
  
  
  if ($iter > $limit) {
    return $edges;
  }

  
    my $sth = $dbh->prepare(qq{
      SELECT e.edge_id, e.to_node_id AS node_id 
      FROM edge e JOIN node n ON e.to_node_id = n.node_id 
      WHERE e.from_node_id = ?
        UNION 
      SELECT e.edge_id, e.from_node_id AS node_id 
      FROM edge e JOIN node n ON e.from_node_id = n.node_id 
      WHERE e.to_node_id = ?
    });
    $sth->execute($node_id, $node_id);
     
    my $res = $sth->fetchall_arrayref({});
    
    push(@$edges, @$res);
    
    foreach my $e (@$res) {
      unless (_seen($seen, [$node_id, $e->{node_id}])) {
        push @$seen, [$node_id, $e->{node_id}];
        _edges(
          dbh        => $dbh, 
          node_id    => $e->{node_id}, 
          node_name  => $e->{node_name}, 
          limit      => $limit, 
          abbreviate => $abbreviate, 
          iter       => $iter, 
          edges      => $edges, 
          seen       => $seen
        );
      }
    }
    $iter++;
  
  return $edges;
}

sub _seen {
  my ($i, $j) = @_;
  
  for (@$i) {
    return 1 if (
      (($_->[0] == $j->[0]) && ($_->[1] == $j->[1])) || 
      (($_->[0] == $j->[1]) && ($_->[1] == $j->[0]))
    );
  }
  
  return 0;
}