You said earlier that you're using something called concurrency control to make sure that multiple people can't make overlapping changes to the same customer account. What about purchase transactions? Some of our customers share the same account between spouses or other family members. If two people use the same account at the same time at different stores, would they both get credit, or would only one transaction be recorded?

You:

That's a good question. Database transactions conform to a property called $,$ which means each transaction on an account must be completed before the next transaction can be processed. This means both transactions will be applied, but only one at a time so there's no mixing of information.