Identifying Entities and Relationships

This section contains the following topics:

Identifying Relationships Among Entities

Overview

By allowing you to document the total picture of an organization's data, the entity-relationship method of performing logical design allows you to:

Use a top-down approach for logical design. To develop an entity-relationship diagram for a database, you define the most general categories of information first. Once you have identified these subject categories, you can then include more specific information in the design.
Demonstrate the semantic meaning of an organization's information. This approach allows you to create a logical design for a database by analyzing descriptions of the organization that are written in everyday English. The entity-relationship diagram, the end product of logical design, accurately reflects the language used by employees to describe the organization. Therefore, this diagram can be reviewed and refined easily.

What are entities and relationships?

As you develop an entity-relationship diagram for a database, you identify each data entity and relationship used by the organization. An entity is a general category of business data that can be easily identified from the available documentation. A relationship defines a logical connection between two associated data entities. For example, the relationship REPORTS TO might identify a connection between a PERSON entity and a COMPANY entity.

Early in the logical design process, you need to determine the data entities and relationships necessary to fulfill the business functions of your organization. This chapter presents guidelines for identifying data entities and their relationships.