[Zope] Unique ID's ?

Hello, After some deep searches about the subject, I found that zope has no real unique ID's. For a particular application (where we can't use the object "url" as an ID as ojects will move), I'd like to assign a unique_id property to each object whenever they are added (the ID must be really really unique). Is there already a patch that do that ? Is there a reason why zope doesn't provide this facility? Thanks in advance, Philippe