Refining the Database Design › Eliminating Unnecessary Entities › Introducing Redundancy

Introducing Redundancy

Although data redundancy should normally be avoided, you can sometimes enhance processing efficiency in selected applications by storing redundant information. A certain amount of planned data redundancy can be used to simplify processing logic.

In some instances, you can eliminate an entity type from the database design by maintaining some redundant information. For example, you might be able to eliminate an entity type by maintaining the information associated with this entity in another entity type in the database. When you merge two or more entity types in this way, you simplify the physical data structures and reduce relationship overhead.

Considerations

Consider maintaining redundant data under the following circumstances:

• An entity type is never processed independently of other entity types. If an entity is always processed with one or more additional entity types, you may be able to eliminate the entity and store the information elsewhere in the database. Since the information associated with the entity is not meaningful by itself, inconsistent copies of the data should not present a problem for the business.
• An entity type is not used as an entry point to the database. If application programs do not use a particular entity type as an entry point to the database, you may be able to eliminate the entity type from the design. However, do not eliminate the entity if it is a junction entity type in a many-to-many relationship.
• The volume of data to be stored redundantly is minimal. Do not maintain large amounts of data redundantly. A high volume of redundant information will require excessive storage space.

Example

The following diagram shows how you might use data redundancy to enhance processing of dental claim information.

By maintaining all DENTIST information with the DENTAL CLAIM entity, you can simplify the database design and reduce the overhead of maintaining the relationship. Since Commonweather users do not process information associated with the DENTIST entity by itself, inconsistent DENTIST information will not present a problem for the business.