about a supermarket database?

Question

how it operates and the description

Answer 1

Any particular database? Items, their UPC's, descriptions and prices? Customers and their purchases if they use the store card? Vendors?

If you're talking about the item database that controls the scanners, there's usually a central database on headquarters computers, that shows item related info and which stores carry the items and prices in each store or area - when changes are made, that info is then downloaded to the computer in the store that controls the scanners. The store itself can also do updates for local items or to fix errors.