Misinterpreting Rules

Writing a rule is not hard. All of us know how to write rules. My mother is an expert in writing rules:

"You must bring a gift when you visit someone's home for the first time."
"You must treat if you go to lunch or dinner with people older than you."
"You must not wash your hair for one month after you give birth." (Yes, it is true … ancient Chinese custom.)

At first I thought I understood what my mother meant, but it was not until many scolding episodes later that I realized my mother's rules were not very clear. For example, I showed up at my Aunt Jane's house for the first time with a handful of cut flowers when my cousin showed up with a beautiful silver platter. My mother was not pleased. She didn't tell me that the gift had to be of a certain value! A year later, when I showed up again at Aunt Jane's house with no gift (because it wasn't the first time any more) and my cousin showed up with a crystal vase, I found out that it was still considered 'the first time' if you hadn't been there in a while. Good Grief!

This is the frustration I had with my mother's rule.

Unfortunately, we encounter the same frustration in the business world. Business rules are often not expressed with the precision you need to guide your work. And when vague rules need to be implemented in systems, this problem is further compounded because computers cannot interpret them.

There are many structured ways of writing rules to help make rules more precise and easy to understand. The BRS RuleSpeak™ Practitioner's Kit provides a set of "Do's and Don'ts" for expressing rules.[1] But I am going to make it even simpler. I am going to tell you two secrets for writing business rules. One is easy, and one is not so easy. If you apply these two secrets, you will have precision in your rules.

The Secrets of Writing Business Rules

Secret #1 (The Easy One)

You must use a 'rule word'. There are really only two rule keywords:

1. must (or should) — including must not (or should not)
2. only — often as in only if

The rule keywords help you compose a rule.

"A shipment can be shipped either by regular post or by express post." is not a rule. It is a statement of fact.
"A shipment must be shipped by either regular post or express post." is a rule.

Again, "A withdrawal can be processed by a teller." is not a rule but rather a statement of fact.
"A withdrawal must be processed by a teller." is a rule.

"A payment over $5,000 can be processed by a manager." is not a rule.
"A payment over $5,000 may be processed only if it has a manager approval." is a rule.

As you can see, the rule keywords structure the statement so that the constraint becomes very clear.

Using rule words is not hard because we, just like my mother, are born knowing how to tell someone to do (or not to do) something. You must do this; you must not do that … it is natural!

Secret #2 (The Hard One)

What is difficult about writing rules is to be very specific about what you must or must not do. The easiest way to do that is to define the terms in your rule.

My mother should have defined 'gift' as "a purchased item over $100." If I had known that, I would have known how to act.

However, you will find that as you define the terms, you will have more questions about a rule. Should every gift be "a purchased item over $100"? When I asked the master of all rules (my mother), I found out that there are different gifts you should send for different occasions. I then found out that there are many different types of gifts. The definitions are:

gift — a purchased item
small gift — a gift under $100
big gift — a gift over $100
special gift — a gift over $250
family special gift — a gift over $500

So, my mother's gift rule should have been, "You must bring a big gift when you visit someone's home for the first time."

Boy! That could get expensive.

Back to my mother, I then found out that 'big gift' only applies to Aunt Jane or someone that is close to the family. I may bring a 'small gift' to casual friends when I visit their homes for the first time. (Thank goodness!) So now I need to know the definition and categorization of 'friend' versus 'family'.

casual friend — a person you have known for less than six months
close friend — a person you have known for a long time, or a person you see and talk to all the time
immediate family — immediate descendants of my parents
extended family — any person related to my parents, excluding immediate family

My mother's gift rule is now, "You must bring a big gift when you visit an extended family member for the first time."

But to make this rule precise, we must challenge "for the first time." I already found out that she really didn't mean "for the first time." A more precise rule would be, "You must bring a big gift when you visit an extended family member you have not visited in the last 12 months."

The wonderful part about having the terms defined is that the rules become more and more easy to write. We recently found out that my sister is pregnant. The Martha Stewart of gift giving (my mother) is overjoyed with the thought of being a grandmother again. Her new rule is, "You must give a family special gift to immediate family on a lifetime special event."

lifetime special event — an event involving marriage, birth, 25th and 50th wedding anniversaries

Four Simple Steps to Adding Precision to Your Rules

The same guideline about precision of terms applies in a business environment. To be precise about a rule, you must have a clear understanding of the terms it references. Consider the following rule:

"An employee must contact a customer if payment for an invoice is not received after 90 days."

This rule may have made perfect sense within the interview or facilitation session where it was discussed. However, while 'employee' might mean an "active full-time Account Receivables employee" for the Operations manager expressing the rule, 'employee' might include 'active', 'inactive', 'fulltime', or 'temporary' employees for a Human Resources manager. Can a 'temporary employee' contact a customer for payment? Can any employee contact a customer for payment? For your customers, 'employee' might be anyone that customer comes in contact with at your company, which might include contractors. Can a contractor contact a customer for payment?

As you can see, until 'employee' has been defined, this rule still produces lots of questions. It makes implementation of this rule uncertain. If a rule needs to be implemented by a computer system, such precision is imperative.

The following four simple steps will help you construct a precise rule:

1. Define all the base terms.
2. Identify and define any subsets from these base terms.
3. Rewrite the rule using the more-specific well-defined terms.
4. Ensure the same term is used by all rules referencing the same concept.

Working Through the Example

Let's apply these steps, working through the example:

"An employee must contact a customer if payment for an invoice is not received after 90 days."

1. Define all base terms.

employee — a person hired by the company
customer — an individual or an organization that purchases the company's goods and services
payment — monetary return in exchange for company's goods and services
invoice — a request for payment
department — a division of the company

2. Identify and Define subsets.

full-time employee — an employee who works at least 40 hours per week
part-time employee — an employee who works less than 40 hours per week
individual customer — a customer that is an individual
corporate customer — a customer that is an organization

3. Rewrite the Rule.

"A full-time employee from the Accounts Receivable Department must contact the customer if payment for an invoice is not received after 90 days."

4. Ensure the same term is used by all rules referencing the same concept.

Here is an example of another rule using the same terms:

"A part-time employee in the Accounts Receivable Department must not process any cash payment."

Just Remember…

Plainly speaking, here are two main things you need to remember when writing a business rule:

• Use rule words to help structure the rule statement: must, should, must not, should not, only, and only if.


• Define the terms so that the rules you write will be clear and precise.

References

[1] Business Rule Solutions' RuleSpeak™ Practitioner's Kit, available as a free download from Business Rule Solutions.

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