Handling transactions?

[EGarrulo <egarrulo@gmail.com>]

What is the Ada idiom to handle transactions in procedures?  I mean, let's suppose we perform the following steps in a procedure:

   Obj_1.A ();
   Obj_2.B ();
   Obj_3.C ();
   Obj_4.D ();

If we don't reach the last line because of an exception, we must undo the effects of any previous actions.  My guess is that you would use a controlled type to embody a transaction, like this pseudo-code:

   Transaction.Start ();
   Obj_1.A ();
   Transaction.Add_Rollback (Rollback_Obj_1_A);
   Obj_2.B ();
   Transaction.Add_Rollback (Rollback_Obj_2_A);
   Obj_3.C ();
   Transaction.Add_Rollback (Rollback_Obj_3_A);
   Obj_4.D ();
   Transaction.Commit (); -- Don't run any registered rollback.

Is this the way it is done, or is it any different?   Thank you.