Another example of throwing data over the wall

Do you know what happens when you have to make an electronic payment but the merchant’s phone hasn’t dialed up to the bank yet? This is what happens (at least in Australia).

1. I swipe my bank card,
2. hit the “SAVINGS” button,
3. type in the amount,
4. I type in my PIN number
5. hit OK
6. the thermal printer prints out the merchant’s copy of the receipt
7. now, the EFTPOS machine dials out to the bank
8. everything I had punched in until now zips down the phone line
9. bank approves transaction
10. the thermal printer prints out the customer’s copy of the receipt
11. end of transaction

By dumbing down the bank’s service interface, the client software ends up with more implementation flexibility, and can design interfaces with different interaction sequence.