The table typically contains values which correspond to boundary or partition input spaces.
The cost aspect makes DDT cheap for automation but expensive for manual testing.
In advanced (mature) automation environments data can be harvested from a running system using a purpose-built custom tool or sniffer, the DDT framework thus performs playback of harvested data producing a powerful automated regression testing tool.
The "user interactions" are replayed through the "new" GUI version and result in the "post test" database.
Anything that has a potential to change (also called "variability," and includes elements such as environment, end points, test data, locations, etc.)