[Zope] Another strategy question

[Robert Leftwich]

On the subject of strategies, thanks for the replies to delivering version 
upgrades, but here is another one -

What is the best strategy to use in maintaining the referential integrity 
of the object database ?
For example, if I have a contact list and an appointment list which needs 
to reference one or more contacts for each appointment and I delete a 
contact, I then need to delete all the appointments that referred to the 
contact.
Is there any low level support for this kind of problem or does it need to 
be built into the app ?

Also, are there any notification functions called when a Folder is modified 
(i.e. items added or deleted) ?

Thanks
Robert Leftwich

PS The answers to this type of question could live in a "Zope Idiom" 
section in the documentation and web site. (I almost said pattern, but 
idiom is more accurate), what do you think ?