reference mode

The way in which a reference restricts the contents of a table field.

A reference can have one of the following reference modes:

• Mandatory

  The field must contain a code that is found the reference table.

• Mandatory unless empty

  The field can be empty. If the field is not empty, the field must contain a code that is found the reference table.

• Not mandatory

  The field can be filled with a code that is not found in the reference table. The reference only serves to expedite queries.