Implied Attributes
Example: when an order is rushed, a new record is made in the rush_order table to store extra facts associated with rushed orders. The nature of the table implies that a certain attribute or fact is present, but because it would have the same value for all rows, the column is not included in the schema. Therefore, the Rush_Order attribute is defined with a constant “Y” instead of a column definition.
In the past, such attributes required dummy columns or views in the database.