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