Application Design: Where to implement historical revisions of objects

Summary:
In a situation where the business model dictates that a certain entity or
class of entities should support the viewing of and differencing of
historical revisions of the data (read properties) contained in the entity
should be supported. Should the logic for the creation and viewing of this
historical information be implemented in the application itself

In Practice:
An application has a model class of "PageContent" which represents the
content that is shown on a certain page. Users of the system are
authenticated, then able to edit the content. From an application design point
of view, where should the logic and underlying system be for the management
of historical revisions.

My specifics include using PHP (5) and Postgre (7.4). I am using the
Table/Row gateways provided by the Zend Framework as a base for my model
objects.
I don't have a large need to remain rdbms-neutral and am fine with a
solution the "locks me in" to using postgre as this will eventually be a
hosted application in a controlled environment.

Option 1 (Implemented in the database/persistence layer):
This would follow the path of logic that stems from seeing the database
as not just a dumb container-- but as the manager and more of a rich
container if you will. When a user updates a certain row (represented as an
entity in the application), the database manages the auditing of the
historical data via triggers (ON UPDATE,ON DELETE) using an audit table with
a similar DDL of the base table, with the addition of audit-specific fields
(like revision id/version/etc). The 'current' version of the data always
remains in the base table, and the application, in its basic functionality,
remains unaware of such functionality, except with the ability to query the
audit table.

Option 2 (Implemented in the Application Layer):
This would see the database as a dumb container, and the model classes on
the application side of 'the boundary' would implement the logic of saving
the revision is a separate table (or potentially in the same table). All the
logic for automagically creating a new revision record on update/delete/etc.
would be handled in the application layer.

Questions:
Which would you choose and why? Outside of (and even including) portability
complaints for the application? From a best practices / theory
point-of-view which is best? Why? Or is the truly a religious debate with
no real right or wrong?

Colin Ross

I have posted this on the zf-general (ZendFramework) and pgsql-php
(Postrge-php) mailing lists to see the differences in views from the two
crowds, abit separately to avoid confusing cross-posting between
communities.