Introduction to Logical Design

This section contains the following topics:

Determining the Corporation's Data Needs

Overview

What is logical database design

Logical database design is the process of determining the logical data structures needed to support an organization's information resource. The logical design process helps you to implement a database that satisfies the requirements of your business organization.

Logical design is critical to the implementation of a corporate database. If your logical design is incomplete or has flaws, making changes to the means of data collection, storage, and protection can be costly later on. By using a well-conceived preliminary design, you can easily implement and test a database. A sound logical design therefore helps to ensure a successful implementation.

A complete and accurate logical design for a database helps to ensure:

Data independence—The logical design process yields a database model that is independent of program or physical storage requirements. This model represents the way data structures appear to users. It does not specify how data structures are maintained in or processed by the computer.
Physical database flexibility—Because the logical design is independent of storage and performance requirements, it can be used to implement a database used with any hardware or software system. During the physical design process, the logical design can be tailored to satisfy the needs of particular users or to suit a particular data processing environment.
Integrity—The logical design identifies both the data maintained in your corporation and the rules of the business. These business rules can be used later to define integrity rules for the physical design.
User satisfaction—The logical design represents data structures in a simple, understandable format. You can show the design to users at any stage of development without intimidating them. The logical design can be easily modified to incorporate users' suggestions and feedback.

There are many viable approaches available for logical database design. In this manual, we combine several design techniques, including systems analysis, the entity-relationship approach, and normalization.

Note: The entity-relationship approach was developed by Peter Chen. For further information on his approach to database design, see Entity-Relationship Approach to Information Modeling and Analysis, Peter P. Chen, editor, ER Institute (1981).

By using these techniques, you can create a logical model that consists of:

Descriptions of the data required by each user application
A comprehensive picture of the corporation's data