This page contains Chapter 3 of the paper "Defining Business Rules ~ What Are They Really?", produced by the Business Rules Group. Other formats in which this paper is available are described in Defining Business Rules -- What Are They Really? (Abstract & Table of Contents)

The subsections in this chapter are:

Defining Business Rules ~ What Are They Really?

Chapter 3 - Formulating Business Rules

The process of identifying business rules is often iterative and heuristic, where rules begin as general statements of policy. Even if the policy is formal and specific, it is typically described in a general and informal fashion, and it often remains for the employees to translate it into meaningful specific statements of what to do.

Yet, even these more specific statements are still often in the nature of 'business ramblings,' without discipline. Indeed, these statements may only sometimes originate in policy. More often, they arise from the day-to-day operation of the organization. As Barbara von Halle explains 'rambling,' <9> it implies "that these sentences are sometimes clear, sometimes (perhaps deliberately) ambiguous, and most of the time, contain more than one idea."

In spite of these shortcomings, 'business ramblings' are usually an analyst's starting point for deriving more formal statements of business rules. Initially, the analyst's assignment is to decompose these composite ramblings into 'atomic' business rules, where each atomic business rule is a specific, formal statement of a single term, fact, derivation, or constraint on the business. Among other things, the analyst should evaluate the stability of the rule. Is it a fundamental aspect of the business, or is it likely to change in the near (or distant) future? Fundamental aspects may be seen in the company's infrastructure, while more transient business rules are often manifested in work practice.

Next, the task is to identify the atomic statement as the definition of a term, fact, constraint, or derivation. Terms, facts, and some of the constraints can be represented directly on graphical models. The remaining constraints and derivations must be translated into some other formalism. This can be as simple as natural language statements or it can have some more formal expression, such as a graphical language like that proposed by Ron Ross. <10> Whatever the form, ultimately the designer will be charged with identifying an appropriate technology for implementing the business rules in an information system.

The Origins of Business Rules -- the Model

Figure 3 shows the first part of the Business Rules conceptual model. (The full model may be found in Appendix A.) In the text above, terms like 'constraint,' 'rule,' and 'business rule' have been used in their conventional English sense. In the descriptions that follow, each of these terms (and others) is given a very precise definition -- critical to the meaning of the model as a whole.

The Origin of Business Rules

Figure 3: The Origin of Business Rules
In the model diagram, we see a policy -- a general statement of direction for an enterprise. Each policy may be composed of more detailed policies, which is to say, a detailed policy may be part of one or more general policies.

An example of a policy for EU-Rent's car rental business might be:

  • "We only rent cars in legal, roadworthy condition to our customers."

A policy may be the basis for one or more business rule statements ('business ramblings'), just as a business rule statement may be based on one or more policies. A business rule statement is a declarative statement of structure or constraint that the business places upon itself or has placed upon it. Each business rule statement may be related to one or more other business rule statements.

For example, each of the following could be a business rule statement for EU-Rent:

  • "Cars should be checked on return from each rental, and on transfer between branches."

  • "If any lights are not working, the bulbs should be replaced. If tires are worn, they should be replaced."

  • "Under any of the following conditions the car should be scheduled for service or repair:
    • accumulated mileage since the last service is greater than 5000,
    • the brakes are not satisfactory,
    • the exhaust is noisy or emitting fumes,
    • there is any damage to body work (apart from superficial dents and scratches), lights or glass,
    • there are any significant fluid leaks."

A business rule statement, in turn, may be the source of one or more (atomic) business rules. Like a business rule statement, a business rule is a statement that defines or constrains some aspect of the business, but (in contrast to a business rule statement) it cannot be broken down or decomposed further into more detailed business rules. If reduced any further, there would be loss of important information about the business. Each business rule may be based on one or more business rule statements.

For example, a business rule for EU-Rent might be:

  • "A car with accumulated mileage greater than 5000 since its last service must be scheduled for service."

It is important to note that an enterprise's business rule applies, regardless of the form used to express it. Business rules have been in place and companies have been responding to them long before anyone ever dreamed of formalizing them or drawing pictures of them. Business rules are an underlying reality in an organization -- independent of an analyst's attempt to structure and describe them.

Note also that each business rule may be expressed in one or more formal rule statements, although each formal rule statement must be an expression of just one (atomic) business rule. A formal rule statement is an expression of a business rule in a specific formal grammar.

A formal rule statement must be in the convention of a particular formal expression type, which is to say one of the formal grammars for representing business rules. Examples of a formal expression type are structured English, IDEF1X, Oracle's CASE*Method, Object Role Modeling, Ross's notation, and so forth.

A structured English example of a formal rule statement is:

    If Car.miles-current-period > 5000 then 
         call Schedule-service(Car.Id)
    End if

Types of Business Rule

Each (atomic) business rule must be one of the following:

Figure 4 shows the part of the business rule model reflecting these ideas. Each of these is described further in subsequent chapters: Chapter 4 (structural assertion), Chapter 5 (action assertion), and Chapter 6 (derivation).

Business Rule Types

Figure 4: Business Rule Types

Definitions

The following summarizes the definitions of the concepts relating to Business Rule.

Business Rule
a statement that defines or constrains some aspect of the business. This must be either a term or fact (described below as a structural assertion), a constraint (described below as an action assertion), or a derivation. It is 'atomic' in that it cannot be broken down or decomposed further into more detailed business rules. If reduced any further, there would be loss of important information about the business.
Business Rule Statement
a declarative statement of structure or constraint that the business places upon itself or has placed upon it.
Formal Expression Type
one of the formal grammars for representing business rules.
Formal Rule Statement
an expression of a business rule in a specific formal grammar.
Policy
a general statement of direction for an enterprise.

Go to... Top of page | Next chapter | Table of Contents | BRG Home Page

Copyright ©2001, the Business Rules Group. All rights reserved.