Identifying Field
An identifying field is a field, or group of fields, that identifies an instance of the entity as unique. For example, the identifying field for an instance of the Sales Order Header entity is Sales Order Number. This field uniquely identifies each instance of the Sales Order Header entity. Suppose you created a report that lists each sales order for the past month. Some sales might have occurred on the same day; others might have shipped on the same day; still others might have been shipped to the same location. The only piece of information that uniquely identifies each sale is the Sales Order Number.