[development] Data-driven database tables andupdates

[Jeff Eaton]

Abstracting certain interactions with SQL is necessary. We do it already
(the pager system, anyone?) when it makes sense. Other parties are
expressing interest in both MSSQL and Oracle implementations for Drupal,
and adding those databases into the mix only makes the problem of schema
definition more apparent.

Writing 'generic' SQL for queries is relatively easy if you're careful.
Writing 'generic' SQL for schema definition is impossible. Thus, schema
definition makes sense as a point of abstraction. Treating it as a
general SQL task ignores the myriad compatability issues between various
DB systems.

That's my $0.02. :)

--Jeff