[Zope] Class - Object relationship

[Tom Cameron]

I would like to know how an object/instance "knows" what class it is built
from.

This may be a silly question, but I just cant see how this works.

The reason I ask, is that I am interested in building a system that may well
involve moving objects from one machine to another and also upgrading
objects from one version of a product to another.

I want to understand more about the "glue" that ties an instance of a
product to the product (ZClass or Python) and the classes it is derived
from.

How much of a python product can I change before the instances of that
product no-longer know that they are instances of that product? Is is just
the meta_type? What if I create two products with the same meta_type?

Where can I read up on this?

TIA
Tom