[Zope] Relational queries on zope obj db?

[Jeff Kowalczyk]

I'm very interested in using zope, but before I dive in, I have a
fundamental question that always presents itself when looking at object
database technologies.

How does a zope developer select related items across folders from the
object store? In effect, I'm asking what ZopeDB can do to feign
relational SQL when it needs a select query on its objects, more
extensive than a simple knock-out filter.

The stumbling block is always the same: 
The problem domain may model perfectly in an ODB's folders/forms, but
then the customer asks for the kind of report that would be a snap in
SQL with any relational database, but is very difficult, or horrendously
slow to do in the object database.

A simple example would be: customer-class in one folder,
purchaseorder-class in another, productitem-class in a third; select all
purchase orders for customerA, displaying each individual productitem
ordered.

Thanks! If there's any way to do SQL-like queries against Zope's Object
Database, or to arrive at the same result, I'm going to check out Zope
very seriously.