NAME

       Graph::Writer - base class for Graph file format writers

SYNOPSIS

         package Graph::Writer::MyFormat;
         use Graph::Writer;
         use vars qw(@ISA);
         @ISA = qw(Graph::Writer);

         sub _write_graph
         {
           my ($self, $graph, $FILE) = @_;

           # write $graph to $FILE
         }

DESCRIPTION

       Graph::Writer is a base class for Graph file format writers.  A particular subclass of
       Graph::Writer will handle a specific file format, and generate a Graph, represented using
       Jarkko Hietaniemi's Graph class.

       You should never create an instance of this class yourself, it is only meant for
       subclassing. If you try to create an instance of Graph::Writer, the constructor will throw
       an exception.

METHODS

   new()
       Constructor - generate a new writer instance. This is a virtual method, or whatever the
       correct lingo is.  You're not meant to call this on the base class, it is inherited by the
       subclasses. Ie if you do something like:

         $writer = Graph::Writer->new();

       It will throw an exception.

   write_graph()
       Read a graph from the specified file:

         $graph = $writer->write_graph($file);

       The $file argument can either be a filename, or a filehandle for a previously opened file.

SUBCLASSING

       To create your own graph format writer, create a module which subclasses Graph::Writer.
       For example, suppose DGF is a directed graph format - create a Graph::Writer::DGF module,
       with the following structure:

         package Graph::Writer::DGF;

         use Graph::Writer;
         use vars qw(@ISA);
         @ISA = qw(Graph::Writer);

         sub _write_graph
         {
           my $self  = shift;
           my $graph = shift;
           my $FILE  = shift;

           while (<$FILE>)
           {
           }

           return 1;
         }

         1;

       Note the leading underscore on the _write_graph() method.  The base class provides the
       public method, and invokes the private method which you're expected to provide, as above.

       If you want to perform additional initialisation at construction time, you can provide an
       _init() method, which will be invoked by the base class's constructor.  You should invoke
       the superclass's initialiser as well, as follows:

         sub _init
         {
           my $self = shift;

           $self->SUPER::_init();

           # your initialisation here
         }

       Someone can then use your class as follows:

         use Graph::Writer::DGF;

         $writer = Graph::Writer::DGF->new();
         $writer->write_graph($graph, 'foo.dgf');

SEE ALSO

       Graph
           Jarkko Hietaniemi's modules for representing directed graphs, available from CPAN
           under modules/by-module/Graph/

       Algorithms in Perl
           The O'Reilly book has a chapter on directed graphs, which is based around Jarkko's
           modules.

       Graph::Writer::Dot
           A simple subclass of this class for writing graphs in the file format used by dot,
           which is part of the graphviz package from AT&T.

       Graph::Writer::VCG
           A simple subclass of this class for writing graphs in the file format used by VCG, a
           tool for visualising directed graphs, initially developed for visualising compiler
           graphs.

       Graph::Writer::XML
           A simple subclass of this class for writing graphs as XML, using a simple graph
           markup.

       Graph::Reader
           A baseclass for Graph file format readers.

AUTHOR

       Neil Bowers <neil@bowers.com>

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.