Order entry clerks use the Orders form to enter the shipping date of an order. Once the shipping date has been entered into the database, the clerks are not allowed to modify it. What property can be set in the Property Palette for the Shipping_Date item to ensure that this data entry restriction is enforced?

The 'Update Only If NULL' property ensures that a field can only be updated when it has no value (is NULL). Once a value is entered, it cannot be modified. This is perfect for the shipping date scenario - clerks can enter the date initially, but once saved, it becomes read-only. 'Enabled' controls whether the item can receive focus, 'Database Item' indicates if it's stored in the database, and 'Update Allowed' is a binary on/off setting.