Business rules

A business rule is “a statement that defines or constrains some aspect of the business.

It is intended to assert business structure or to control or influence the behavior of the

business . . . rules prevent, cause, or suggest things to happen” (GUIDE Business Rules

Project, 1997). For example, the following two statements are common expressions of

business rules that affect data processing and storage:

• “A student may register for a section of a course only if he or she has successfully

completed the prerequisites for that course.”

• “A preferred customer qualifies for a 10 percent discount, unless he has an overdue account balance.”

Most organizations (and their employees) today are guided by thousands of combinations of such rules. In the aggregate, these rules influence behavior and determine

how the organization responds to its environment (Gottesdiener, 1997; von Halle, 1997).

Capturing and documenting business rules is an important, complex task. Thoroughly

capturing and structuring business rules, then enforcing them through database technologies, helps ensure that information systems work right and that users of the information understand what they enter and see.

THE BUSINESS RULES PARADIGM The concept of business rules has been used in information systems for some time. There are many software products that help organizations manage their business rules (for example, JRules from ILOG, an IBM company). In

the database world, it has been more common to use the related term integrity constraint

when referring to such rules. The intent of this term is somewhat more limited in scope,

usually referring to maintaining valid data values and relationships in the database.

A business rules approach is based on the following premises:

• Business rules are a core concept in an enterprise because they are an expression

of business policy and guide individual and aggregate behavior. Well-structured

business rules can be stated in natural language for end users and in a data model

for systems developers.

• Business rules can be expressed in terms that are familiar to end users. Thus, users

can define and then maintain their own rules.

• Business rules are highly maintainable. They are stored in a central repository, and

each rule is expressed only once, then shared throughout the organization. Each systems.

Scope of Business Rules

In this chapter and the next, we are concerned with business rules that impact only an

organization’s databases. Most organizations have a host of rules and/or policies that

fall outside this definition. For example, the rule “Friday is business casual dress day”

may be an important policy statement, but it has no immediate impact on databases. In

contrast, the rule “A student may register for a section of a course only if he or she has

successfully completed the prerequisites for that course” is within our scope because

it constrains the transactions that may be processed against the database. In particular, it causes any transaction that attempts to register a student who does not have the

necessary prerequisites to be rejected. Some business rules cannot be represented in

common data modeling notation; those rules that cannot be represented in a variation

of an entity-relationship diagram are stated in natural language, and some can be

represented in the relational data model, which we describe in Chapter 4.

GOOD BUSINESS RULES Whether stated in natural language, a structured data model,

or other information systems documentation, a business rule will have certain characteristics if it is to be consistent with the premises outlined previously. These characteristics are summarized in Table 2-1. These characteristics will have a better chance of being

satisfied if a business rule is defined, approved, and owned by business, not technical,

people. Businesspeople become stewards of the business rules. You, as the database

analyst, facilitate the surfacing of the rules and the transformation of ill-stated rules into

ones that satisfy the desired characteristics.

TABLE 2-1 Characteristics of a Good Business Rule

Characteristic Explanation

Declarative A business rule is a statement of policy, not how policy is enforced or conducted; the rule

Hoffer, Jeffrey A.; Venkataraman, Ramesh; Topi, Heikki (2012-07-12). Modern Database Management (11th Edition) (Page 62). Pearson HE, Inc.. Kindle Edition.