Access Layer

I'm still new to pure OO-Design but have read al the threads about
business objects, many articles on design patterns especially Wolfgang
Keller's articles on mapping objects to tables and relational database
access layers,etc.  I must say after days of just reading some
abstractions are starting to make sense.

I've also seen many requests for existing frameworks in code - they
seem quite rare.  I would like to narrow the request for such a
framework down to specifically the access layer (logical and physical
layers).  Business objects are quite unique in design but surely how
business objects are made persistent must be available in a reusable
framework.  The things that I find difficult to express in code are
objects like Transaction, Connections, Object Cache, Connection/Query
Broker's.  The Datamanager object itself I somewhat understand, but
for implementation of the rest some code example will help a lot.