NAME

       Graph::Reader - base class for Graph file format readers

SYNOPSIS

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

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

           # read $FILE and populate $graph
         }

DESCRIPTION

       Graph::Reader is a base class for Graph file format readers.  A particular subclass of
       Graph::Reader 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::Reader, the constructor will throw
       an exception.

METHODS

   new()
       Constructor - generate a new reader 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:

         $reader = Graph::Reader->new();

       It will throw an exception.

   read_graph()
       Read a graph from the specified file:

         $graph = $reader->read_graph($file);

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

SUBCLASSING

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

         package Graph::Reader::DGF;

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

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

           while (<$FILE>)
           {
           }

           return 1;
         }

         1;

       Note the leading underscore on the _read_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::Reader::DGF;

         $reader = Graph::Reader::DGF->new();
         $graph = $reader->read_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
           This O'Reilly book has a chapter on directed graphs, which is based around Jarkko's
           modules.

       Graph::Reader::XML
           A simple subclass of this class for reading a simple XML format for directed graphs.

       Graph::Writer
           A baseclass for Graph file format writers.

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.