[ZODB-Dev] What is meant by 'using RDMBS as the back-end storage'?

[Jeff Kowalczyk]

When articles mention that Zope's ODB can now "use a variety of back-end
storages, including RDBMS'", are they referring to:

The the ability to connect to and query *external* existing data tables
in mySQL, postgres, and others, and query that with ZSQL

-or- 

are some users' Zopes configured to flatten the object store directly
into an RDBMS as the primary storage, instead of zope's customary
'database file'. Could you not query this with SQL from within Zope to
do ad-hoc reporting?

>From previous responses, I would guess the former, but why do they then
call it a back-end storage, instead of an 'external connection to
RDBMS'?

I'm trying to gather current information and near-term development
roadmaps to decide how well I can simulate some familiar SQL
use-patterns for reports. This will be the deciding factor on whether I
can start some of my next intranet-app projects in Zope.