When you have a number of Records entered into a Table, the issue arises of how to identify them. The classical relational database model does this by defining a field as a Primary Key. The concept is that each Record's Primary Key is unique, and so by specifying a particular value for a Primary Key the system can identify the record.
The neatComponents system does not need you to specify a Primary Key for a Table, as it does this behind-the-scenes – creating a Record ID field. This is normally invisible, but if you do need to expose the Record ID (useful for some types of Query), you can add a field with a Record ID datatype and it will display the value.
Since Record IDs are numbers, they may be useful for computers, but are not human-friendly. The neatComponents system therefore allows you to specify an alternative field (or combination of fields) to be used whenever a pick-list of records is shown.