12. What is NULL and how is it used in MDM?
b. Data marker
NULL is a special data marker. It denotes missing or not populated yet data. It can't be treated as an existing value and doesn't participate in equations of uniqueness integrity. That is, multiple records are permitted to have NULL for a unique field. To prevent records from having these undefined records, use validation functions IS_NULL and IS_NOT_NULL. Also, nulls can be handled through import manager.