If you pick sbsets of the transaction, then cassandra is ACID in part because it guarantees that a write leaves an entry in a node's log. A banking system only guarantees a log of all increments and decrements, not agreement of the current balance throughout the system. So, as a whole, the system is definitely BASE and not ACID.
So we're back to a boundary argument, again. Partisans will draw the boundaries as it suits their argument.
Though, I do need to emphasise a point:
> subsets of the transaction
Each step in moving the information from the ATM to the General Ledger is itself a transaction. There are no "subsets of a transaction". If it's divisible, then it's not a transaction (this is the atomicity requirement of ACID).
Yes, each step is a transaction, but the whole is not consistent at any one moment. Availability was chosen over consistency all the way up.
We see this pattern all over the place. The primary example is any place that accepts checks as payment. Availability is immediate, but consistency is not necessarily there.
You see it with a business making a PO. Lots of places will still take credit cards which are only processed daily (ok, this is becoming rare where there is cell service.)
