Entity Identifier
Each object has an identity that characterizes its existence. The identifier provides an unambiguous way to distinguish any object in an entity. It is one way to distinguish between two objects with identical attribute values.
An identifier consists of one or several mandatory attributes or roles that enable unique identification of an entity.
Customer number 2718 executes Reservation number 314159.
Each entity has a unique identifier whose value can be used to find each of its instances.
By default, the identifier is implicit. In this case a primary key will be automatically generated from the entity name.
Identification by an attribute
It is also possible to select one of the attributes of the entity as its identifier. To do this:
1. Open properties of the entity.
2. Click the drop-down list then Attributes.
The list of attributes appears.
3. For the chosen attribute, select "Yes" in the Identifier column.