Question

What is the difference between data redundancy and data inconsistency?

Answer 1

Redundancy is data that is not needed or no longer needed. Inconsistency is where you have different data for what should be the same thing, as a result of one piece of data having a few copies and not all of them being updated. So if someone's address is on a system several times, and then their address changes, but it is only updated in some of those places, then the person will have both their old and new address on the system. The data is not consistent then. To avoid this data should be only stored once and everyone that needs it looks at the one set, rather than each having their own copy.