Chapter 5, Problem 1RQ

Explanation of Solution

Entity Supertype:

• The entity supertype is an entity type that has the relation with one or more subtypes and it contains the common attributes of its subtypes.
• The entity subtype is a grouping of entities type in single entity that shares the common attributes or relationships which are different from other grouping.

Use of entity supertype:

The reason for using entity supertype is to reduce redundant relationships and also reduce the number of nulls.

Example:

The following example demonstrates the “supertype” entity, “subtype” entity, and “discriminator”.

Explanation:

• Here, “Employee” entity is a “supertype” entity.
• “Hourly Employee”, “Salaried Employee”, and “Consultant” are the “Sub type” entities.
• “Emp_type” is a discriminator to select appropriate “subtype”.