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#
# Graph::Writer::XML - write a directed graph out as XML
#
package Graph::Writer::XML;
$Graph::Writer::XML::VERSION = '2.10';
use 5.006;
use strict;
use warnings;
use parent 'Graph::Writer';
use XML::Writer;
#=======================================================================
#
# _write_graph() - perform the writing of the graph
#
# This is invoked from the public write_graph() method,
# and is where the actual writing of the graph happens.
#
# Basically we start a graph element then:
#       [] dump out any attributes of the graph
#       [] dump out all vertices, with any attributes of each vertex
#       [] dump out all edges, with any attributes of each edge
# And then close the graph element. Ta da!
#
#=======================================================================
sub _write_graph
{
    my $self  = shift;
    my $graph = shift;
    my $FILE  = shift;
    my $v;
    my $from;
    my $to;
    my $aref;
    my $xmlwriter;
    $xmlwriter = XML::Writer->new(OUTPUT      => $FILE,
                                  DATA_MODE   => 1,
                                  DATA_INDENT => 2);
    $xmlwriter->setOutput($FILE);
    $xmlwriter->startTag('graph');
    #-------------------------------------------------------------------
    # dump out attributes of the graph, if it has any
    #-------------------------------------------------------------------
    $aref = $graph->get_graph_attributes();
    foreach my $attr (keys %{ $aref })
    {
        $xmlwriter->emptyTag('attribute', 
                                'name' => $attr,
                                'value' => $aref->{$attr});
    }
    #-------------------------------------------------------------------
    # dump out vertices of the graph, including any attributes
    #-------------------------------------------------------------------
    foreach $v (sort $graph->vertices)
    {
        $aref = $graph->get_vertex_attributes($v);
        if (keys(%{ $aref }) > 0)
        {
            $xmlwriter->startTag('node', 'id' => $v);
            foreach my $attr (keys %{ $aref })
            {
                $xmlwriter->emptyTag('attribute', 
                                        'name' => $attr,
                                        'value' => $aref->{$attr});
            }
            $xmlwriter->endTag('node');
        }
        else
        {
            $xmlwriter->emptyTag('node', 'id' => $v);
        }
    }
    #-------------------------------------------------------------------
    # dump out edges of the graph, including any attributes
    #-------------------------------------------------------------------
    foreach my $edge (sort _by_vertex $graph->edges)
    {
        ($from, $to) = @$edge;
        $aref = $graph->get_edge_attributes($from, $to);
        if (keys(%{ $aref }) > 0)
        {
            $xmlwriter->startTag('edge', 'from' => $from, 'to' => $to);
            foreach my $attr (keys %{ $aref })
            {
                $xmlwriter->emptyTag('attribute', 
                                        'name' => $attr,
                                        'value' => $aref->{$attr});
            }
            $xmlwriter->endTag('edge');
        }
        else
        {
            $xmlwriter->emptyTag('edge', 'from' => $from, 'to' => $to);
        }
    }
    $xmlwriter->endTag('graph');
    $xmlwriter->end();
    return 1;
}
sub _by_vertex
{
    return $a->[0].$a->[1] cmp $b->[0].$b->[1];
}
1;
__END__
HideShow 95 lines of Pod
=head1 NAME
Graph::Writer::XML - write out directed graph as XML
=head1 SYNOPSIS
    use Graph;
    use Graph::Writer::XML;
    $graph = Graph->new();
    # add edges and nodes to the graph
    $writer = Graph::Writer::XML->new();
    $writer->write_graph($graph, 'mygraph.xml');
=head1 DESCRIPTION
B<Graph::Writer::XML> is a class for writing out a directed graph
in a simple XML format.
The graph must be an instance of the Graph class, which is
actually a set of classes developed by Jarkko Hietaniemi.
The XML format is designed to support the Graph classes:
it can be used to represent a single graph with a collection
of nodes, and edges between those nodes.
The graph, nodes, and edges can all have attributes specified,
where an attribute is a (name,value) pair, with the value being scalar.
=head1 METHODS
=head2 new()
Constructor - generate a new writer instance.
    $writer = Graph::Writer::XML->new();
This doesn't take any arguments.
=head2 write_graph()
Write a specific graph to a named file:
    $writer->write_graph($graph, $file);
The C<$file> argument can either be a filename,
or a filehandle for a previously opened file.
=head1 KNOWN BUGS
Attribute values must be scalar. If they're not, well,
you're on your own.
=head1 SEE ALSO
=over 4
=item L<XML::Writer>
The perl module used to actually write out the XML.
It handles entities etc.
=item L<Graph>
Jarkko Hietaniemi's modules for representing directed graphs,
available from CPAN under modules/by-module/Graph/
=item Algorithms in Perl
The O'Reilly book which has a chapter on directed graphs,
which is based around Jarkko's modules.
=item L<Graph::Writer>
The base-class for Graph::Writer::XML
=back
=head1 REPOSITORY
L<https://github.com/neilb/Graph-ReadWrite>
=head1 AUTHOR
Neil Bowers E<lt>neil@bowers.comE<gt>
=head1 COPYRIGHT
Copyright (c) 2001-2012, Neil Bowers. All rights reserved.
Copyright (c) 2001, Canon Research Centre Europe. All rights reserved.
This script is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
=cut