Chapter 4 Building Conceptual Data Models

Defining inheritances in a CDM

Inheritance allows you to define an entity as a special case of a more general entity. The entities involved in an inheritance have many similar characteristics but are nonetheless different. The general entity is known as a supertype (or parent) entity and contains all of the common characteristics. The special case entity is known as a subtype (or child), entity and contains all of the particular characteristics.

Between entities, it is also possible to define an inheritance link. In an inheritance link, one or more subtype (or child) entities inherit, at the physical level, all or part of the entity attributes carried by one supertype (or parent) entity.

The Account entity below represents all the bank accounts in the information system. It includes two subtypes: checking accounts and savings accounts. The notion of inheritance represents the entities Checking and Savings as specialized types of the parent entity Account.