NAME

       Algorithm::Dependency::Source - Implements a source of heirachy items

DESCRIPTION

       The Algorithm::Dependency::Source class provides an abstract parent class for implementing
       sources for the heirachy data the algorithm will use. For an example of an implementation
       of this, see Algorithm::Dependency::Source::File, which is bundled with the main
       Algorithm::Dependency package.

METHODS

   new @arguments
       Although you cannot directly use the "new" constructor for
       "Algorithm::Dependency::Source", it will work the same in all subclasses.

       The constructor takes zero or more subclass specific arguments to define the location of
       the source of the items, and returns a new object. Alrough it may check that the arguments
       you passed are valid, the source will usually NOT actually load the items from the source,
       instead defering the loading until you need to use the items.

       Returns a new object on success, or "undef" on error.

   load
       The "load" method is the public method used to actually load the items from their storage
       location into the the source object. The method will automatically called, as needed, in
       most circumstances. You would generally only want to use "load" manually if you think
       there may be some uncertainty that the source will load correctly, and want to check it
       will work.

       Returns true if the items are loaded successfully, or "undef" on error.

   item $name
       The "item" method fetches and returns the item object specified by the name argument.

       Returns an Algorithm::Dependency::Item object on success, or "undef" if the named item
       does not exist in the source.

   items
       The "items" method returns, as a list of objects, all of the items contained in the
       source. The item objects will be returned in the same order as that in the storage
       location.

       Returns a list of Algorithm::Dependency::Item objects on success, or "undef" on error.

   missing_dependencies
       By default, we are leniant with missing dependencies if the item is neved used. For
       systems where having a missing dependency can be very bad, the "missing_dependencies"
       method checks all Items to make sure their dependencies exist.

       If there are any missing dependencies, returns a reference to an array of their ids. If
       there are no missing dependencies, returns 0. Returns "undef" on error.

EXTENDING

       "Algorithm::Dependency::Source" itself is a fairly thin module, and it is intended that
       you will probably need to extend it to be able to extract item data from whatever location
       you have stored them.

       This is usually a fairly simple two step process.

       Overload the "new" method.
           Assuming your subclass takes some form or argument on creation, you will need to
           overload the "new" method to accept the arguments, validate them, and store them in
           the source object.

       Define the method "_load_item_list".
           Leaving our parent's "load" method to take care of conflict, errors, and whatever, the
           "_load_item_list" method is used to simply create a list of
           Algorithm::Dependency::Item objects from wherever you store the item, and return them
           as a list.

       Having completed these two things, your subclass should be completed. For an example of
       the code, have a look at the source for the simple subclass
       Algorithm::Dependency::Source::File.

SUPPORT

       For general comments, contact the author.

       To file a bug against this module, in a way you can keep track of, see the CPAN bug
       tracking system.

       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Algorithm-Dependency>

AUTHOR

       Adam Kennedy <adamk@cpan.org>

SEE ALSO

       Algorithm::Dependency, Algorithm::Dependency::Source::File

COPYRIGHT

       Copyright 2003 - 2009 Adam Kennedy.

       This program is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

       The full text of the license can be found in the LICENSE file included with this module.