Data::Package - Base class for packages that are purely data


  ### Using a Data::Package
  use Global::Config;
  # Get the data in the default or a prefered format
  # Can we get the data in a particular format?
  ### Creating a data package
  package Global::Config;
  use strict;
  use base 'Data::Package';
  use Config::Tiny ();
  # Load and return the data as a Config::Tiny object.
  sub __as_Config_Tiny {
        local $/;


In the CPAN, a variety of different mechanisms are used by a variety of different authors in order to provide medium to large amounts of data to support the functionality contained in theirs or other people's modules.

In this author's opinion these mechanisms are almost never clean and elegant and are often quite ugly. One of the worst examples was a module that converted the Arial font into a 2.7meg perl module.

Why exactly the authors are having to resort to these measures is often unclear, although I suspect it is primarily the ease with which modules can be found (compared to data files). Regardless, one thing is very clear.

There is no obvious, easy and universal way in which to create and deliver a "Data Product" via CPAN. A data product is a package in where there is little or more likely no functionality or code, and all of the "value" in the package is contained in the data itself.

Within the global and unique namespace of perl, most of the packages represent code in the form of APIs. However this does not mean that code is the only thing that is capable of reserving a package name.


Data::Package provides the core of what is hoped will be a highly scalable and extendable API to create data packages and data products that can be delivered via the CPAN (and thus anywhere else).

It provides a minimal API that separates how the developer obtains the data in their code from the methods by which the data is actually obtained, installed, loaded, parsed and accessed.

The intent is that the consumer of the data should not have to know or care how the data is obtained, just that they are always able to obtain the data when they want in the format they want.

It also allows the author or provider of the data to assign the data to a unique location within the perl namespace. The can then change or improve the underlying install, storage and loading mechanisms without the need for any code using that data to have to be changed.

API Overview

The core Data::Package API requires that only only two static methods be defined, and probably only one matters if you wrote both the data package, and code that is using it.

In the simplest and (probably) most common case, where the data package returns only a single known object type, you should only have to load the module and then get the data from it.

  use My::Data::Package;
  $Data = My::Data::Package->get;

For more complex cases where the data package is capable of providing the data in several formats, you can use the provides method to find out what types of object the data package is capable of providing.

  @classes = My::Data::Package->provides;

Your code will most likely simply be confirming that the data is available in a particular format. Once you know you are able to get it in the format that you want, you can simple do the following.

  $Data = My::Data::Package->get('Object::Type');


The current implementation is considered to be a proof of concept only.

It should work, and I do want to know about bugs, but it's a little early to be relying on it yet for production work. It does not have a sufficiently complete unit test library for starters.

About half the implementation is done by pulling in functionality from other dependant modules, which are not completely production-standard themselves (in the case of Params::Coerce. For a proper production grade version, we probably shouldn't have any dependencies.

However, the API itself is stable and final, and you can write code that uses this package safely, and any upgrades down the line should not affect it.



The new constructor is provided mainly as a convenience, and to let you create handles to the data that can be passed around easily.

Takes no arguments, and returns a new blessed object of the same class that you called it for.

provides [ $class ]

The provides method is used to find the list of formats the data package is capable of providing the data in, although typically it is just going to be one.

When called without an argument, the method returns a list of all of the classes that the data can be provides as instantiated objects of.

In this first version, it is assumed you are providing the data as some form of object.

If provided an argument, the list will be filtered to list only those that are of the object type you specificied. This can be used to either limit the list, or check for a specific class you want.

In both cases, the first class returned by provides is the same that will be returned by the get method when called with the same (or without an) argument.

And either way, the method returns the classes in list context, or the number of classes in scalar context. This also lets you do things like:

  if ( Data::Thingy->provides('Big::Thing') ) {
        die "Data::Thingy cannot provide a Big::Thing";

get [ $class ]

The get method does whatever is necesary to access and load the data product, and returns it as an object.

If the data package is capable of providing the data in more than one format, you can optionally provide an object of the class that you want it in.

Returns an object (possibly of a class you specify) or undef if it is unable to load the data, or it cannot provide the data in the format that you have requested.


Bugs should always be submitted via the CPAN bug tracker

For other issues, contact the maintainer


Adam Kennedy <>


Copyright 2005-2007 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.