Content versioning for Plone2 (0.1.3)

Ever get frusted when you, as a non-manager content editor of Plone, have to retract an object in a published state before they are able to edit it? This product is the answer! It let you make changes to a copy of the published object, while leaving the original published version untouched. When the new version is approved and published, it takes the place of the previously published version. This allows a "quiet" workflow to take place behind the published version, without the need to retract it.

PVSForPlone2 (Portal content Versioning System for Plone2) is a Zope product for use within Plone2 instances. It is the result of our frustration with the current limitations of the workflow mechanism: a user has to retract an object  in a published state before they are able to edit it (unless the user is a Manager).

Our solution was to extend the workflow mechanism with versioning capabilities. The basic idea is to let low-level (or mid-level) users make their changes to a copy of the published object, while leaving the original published version untouched. When the new version is approved and published, it takes the place of the previously published version. This allows a "quiet" workflow to take place behind the published version, without the need to retract it.

This product introduces a new permission, 'Create version'. Users with this permission can still bring up the edit form of an object even though they do not have the permission to modify it (such as in 'published' or 'pending' state). When the edit form is submitted, the changes are not saved to the
original object, but saved to a new copy instead, created transparently by this product.

This copy is a new version of the original object, and will go through the same publishing workflow process as the original. When the new version is approved and published, the system will again transparently replace the original object with the new version.

This product also extends Plone2 objects with version management functionality, providing a complete versioning service. Users can see the evolution of a certain object, and Manager/Reviewer users can republish a previous version at any time. Further, anyone who can see the previous
versions can choose to create a new version based on any of the old ones.

The product should work right out of the box, and by default, allow owners to create versions. It also works on most default content types.

Developers familiar with workflow creation will find this product helpful for creating some interesting workflows, such as the one we developed for a government agency to preserve the paper trails of their documents. However, the following should be kept in mind during workflow development:

• All versions, other than the one with the original id, are hidden from the 'folder contents' view, the ZMI and so on. Users can delete or move an object without the fear of leaving hidden versions dangling behind; but when copying, only the 'published' (or 'curent') version is copied.
• When the system creates a new version, the system will set the current user as the owner, so it's possible to let users of different roles join the editing process.
• It expects that the object's associated workflow has a defined transition called 'publish'.
• As a published object being replaced by another version, the system will first look for a transition called 'archive' in the object's workflow definition, and perform that transition. If no such transition is found, it will put the object into the default state.
• The 'Modify content' permission overrides 'Create versions' permission. So if a user has both 'modify content' permission and 'create versions' permission over an object, no versioning feature is provided.

Also, when installing new Plone product, make sure its editing action points to a script whose ID is of this format xxx_edit_form. And the ID of the script that saves the changes follows the pattern xxx_edit.