How can a POS terminal determine if a coupon is valid?
<p>This is something I have always wondered about. Coupons can be very touchy when it comes to their requirements, like:</p>

<ul>
<li>Expiration date</li>
<li>Item quantity requirements</li>
<li>Which items are eligible</li>
<li>Can involve multiple groups of items (e.g., "Buy X number of items from this group, get an item from another group free/money off/percent off")</li>
</ul>

<p>I know that the GS1 DataBar can hold a lot more information like this, but I'd imagine that only goes so far.</p>

<p>How does a POS terminal determine whether a scanned coupon is valid or not? Is some kind of supplemental information stored in a database somewhere?</p>