If all the mileage account(earned and redeemed) are stored in FFMS, then I can't understand why there's a Mileage Account in BDOM. I am a bit hesitant to take it off from the class diagram also, since that would be like changing the BDOM. The only time FBN connects to FFMS is to check whether the customer has got enough miles to pay for the Itinerary or not.
Can I safely assume that there will be some backend process that runs and updates the FBN mileage account from the FFMS system, and the customer can then check his mileage by logging to the FBN site ???
Well, you can assume anything you want with the assignment as the architect - just document it.
That being said... I'd recommend reading the requirements carefully a few times before you decide on one solution over another. As stated in the documentation Sun provides, you're not allowed to rewrite the FFMS - they just did that "six months prior" and aren't interested. But obviously, you're going to have to do something to allow for reward travel in some means other than the current system of checking it across two different systems.
Just some food for thought, and trying not to bias you one way or another.
Theodore Jonathan Casser
SCJP/SCSNI/SCBCD/SCWCD/SCDJWS/SCMAD/SCEA/MCTS/MCPD... and so many more letters than you can shake a stick at!