Archetypes (formerly known as CMFTypes) is a ZopeApplicationServer Product which simplifies the creation of new content types under Zope 2 
and the Content Management Framework (CMF). A content type might be a document, event, image, or any other content object that is made 
available for users/content creators to add to a Zope content management site. Most content management projects involve introducing 
new types of content, which can be both time consuming and complicated. Archetypes provides a simple, extensible framework that can 
ease both the development and maintenance costs of CMF content types while reducing the learning curve for the simpler cases.

The creation of a new Type using Archetypes involves a main text file (python) that defines the fields and other objects within 
your type, their properties, and their behavior. Archetypes uses this information to auto generate on demand all forms and pages 
needed to add, edit, and view your types data. When you have written this file, you then have a product that you would install 
just like any other CMF/Plone product.

* http://zope.org
* http://plone.org
* http://plone.org/documentation/archetypes/
* http://sourceforge.net/projects/archetypes/

ArchGenXML is a commandline utility that generates Plone applications (products) based on the Archetypes 
framework from UML models using XMI (.xmi, .zargo, .zuml) and XSD (XMLSchema) files.

Design your Archetypes (code for content objects in plone) offline using a UML design tool like Poseidon or ObjectDomain. 
Export the UML to XMI or XSD and use ArchGenXML to generate Phyton code for use as a Product. 
This new Product is available as a new item (document) type in the Plone userinterface.

This time the tool is not round-trip enabled -- generated code can't be back-converted into XMI. But you can re-generate over existing code -- the Method bodies are kept.

http://plone.org/documentation/archetypes/archgenxml-manual