boundary between DAS and SDO implementation

[Coller, Shmuel]

It is not clear to me if Tuscany implementation for SDO  has a well defined 
boundary where one can plug a self written DAS.
I am interested to learn this issue -  also at the level of SDO specs by Oasis 
TC .
For example - are there Java interfaces that a DAS should implement so that a 
DAS can  serve alongside (and reuse) an available  SDO implementation ?
Shmuel Coller