[Zope] ZPatterns Question

[RC Compaan]

I created a ZClass called "Product" with Dataskin as baseclass.

I also added a specialist called ProductManager containing a default rack.
Under storage for the rack I selected the newly created Product ZClass.

My product ZClass needs to query both a RDBMS and the ZODB for
attributevalues.  At this point I get lost.
I guess i should add an attributeprovider plug-in???

What should go into the fromexpr and attrsexprs properties of the
attributeprovider?  Should one add an attributeprovider for each attribute
of the product?

Roché