Key Types

Whenever you create an entity in your data model, one of the most important questions to ask is: �How can a unique instance be identified?� To develop a correct logical data model, you uniquely identify each instance in an entity.

In each entity in a data model, a horizontal line separates the attributes into two groups, key areas and nonkey areas. The area above the line is the key area, and the area below the line is the nonkey area, or data area. The key area of CUSTOMER contains �customer id� and the data area contains �customer name,� �customer address,� and �customer phone.�