Database Systems: Design, Implementation, & Management
Database Systems: Design, Implementation, & Management
13th Edition
ISBN: 9781337627900
Author: Carlos Coronel, Steven Morris
Publisher: Cengage Learning
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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”.

Database Systems: Design, Implementation, & Management, Chapter 5, Problem 1RQ

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”.

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