Chris Jones has posted a guide to upgrading you PHP apps with as little downtime as possible via the new Editioning feature the 11gR2 version of the database.

The Editioning feature of Oracle Database 11gR2 is ideal for web sites that aim for no downtime when releasing application enhancements. Editioning allows certain database objects to have multiple versions all available at the same time. Applications can decide at runtime which version of the objects should be used.

He gives an example of a simple PHP application - an hours tracking app. He creates a stored function that calculates the number of days of vacation an employee can have and shows how to create a new "edition" of it with updated calculations. Your script then runs an alter on the session to point the edition to this new version.