Account id in Balance Enquiry Model?

How this accountId in BalanceEnquiry model differs from accountNumber in Account model?

Hi Gaurav,
good question, if you think about it to check the balance in an account you need first to know which account to check first right, so use the account id to know if the customer asking about her/his checking account/ saving account.
I hope this helps you to understand the point of accountId

@Design_Gurus do you agree?