[Zope] Will the inheritance relationship will be preserved after export/import?

Hi, Suppose Product P1 is a subclass of Product P, and M is a method of P, so that we can call both P.M and P1.M Then, P and P1 were exported from Data1.fs (Host A) , and imported to Data2.fs (Host B). Now, let's move to the Host B, and modified the content of M. and create an instance of Product P as p and Product P1 as p1. It should be that p.M and p1.M execute the same code (new content o f M). But it is not. p1.M execute the old code of M which is the same as it used to be in Host A. The interitance relationship seems broken after export/import between different ZODB. How can I rebuid the relationship between P and P1? Thanks. Iap