04/06/2023
Database System: �
Business Rules
When database designers go about
selecting or determining the entities,
attributes, and relationships that will be
used to build a data model, they might
start by gaining a thorough
understanding of what types of data exist
in an organization, how the data is used,
and in what time frames it is used. But
such data and information do not, by
themselves, yield the required
understanding of the total business.
From a database point of view, the
collection of data becomes meaningful
only when it refects properly defned
business rules. A business rule is a brief,
precise, and unambiguous description of
a policy, procedure, or principle within a
specifc organization. In a sense, business
rules are misnamed: they apply to any
organization, large or small—a business,
a government unit, a religious group, or a
research laboratory—that stores and uses
data to generate information.
Business rules derived from a detailed
description of an organization’s
operations help to create and enforce �
actions within that organization’s
environment. Business rules must be
rendered in writing and updated to
refect any change in the organization’s
operational environment.�
Properly written business rules are used
to defne entities, attributes, relationships,
and constraints. Any time you see
relationship statements such as “an agent
can serve many customers, and each
customer can be served by only one agent,”
business rules are at work. You will see the
application of business rules throughout
this book, especially in the chapters
devoted to data modeling and database � To be efective, business rules must be
easy to understand and widely
disseminated to ensure that every person
in the organization shares a common
interpretation of the rules. Business rules
describe, in simple language, the main
and distinguishing characteristics of the
data as viewed by the company. Examples
of business rules are as follows:• A
customer may generate many invoices.•
An invoice is generated by only one
customer.• A training session cannot be
scheduled for fewer than 10 employees or
for more than
30 employees.�
Note that those business rules establish
entities, relationships, and constraints.
For example, the frst two business rules
establish two entities (CUSTOMER and
INVOICE) and a 1:M relationship
between those two entities. Te third
business rule establishes a constraint (no
fewer than 10 people