Thomas Guettler wrote:

I think it is enough to agree on a method name, no need to create an Interface.

Behaviour must also be agreed upon. For example: - return 0 if no upgrade needed - return 1 of upgrade succeeded - raise an exception if upgrade failed Otherwise you won't know how to behave with the function. Other than that there isn't much interfacing to do. :) Well, it could be nice to agree on the attribute for object version info too.