Being Complete in Expressing Rules

Ronald G.  Ross
Ronald G. Ross Co-Founder & Principal, Business Rule Solutions, LLC , Executive Editor, Business Rules Journal and Co-Chair, Building Business Capability (BBC) Read Author Bio       || Read All Articles by Ronald G. Ross

Extracted from Rules: Shaping Behavior and Knowledge, by Ronald G. Ross, 2023, 274 pp,


Suppose you are in an airport, about to pass through security. You see a posted sign that says:

Sign Posted at Entrance to Airport Security: No Photography

The sign clearly doesn't mean no photography anywhere in the universe. It means no photography in airport security. How do we know? Context provides the clues. We happen to be standing right at that entrance.

Then we proceed into security and we see a sign that says:

Sign in Security: Jokes will be taken seriously.

Seriously?! Joking is now literally banned in the whole universe? How sad! No, we are in the context of security. They just mean there.

Suppose we are in a video conference. The moderator says:

Video Conference Rule: All participants should be muted while not speaking.

Wait! I don't actually have a mute button on my person. So, they must mean the mute button on the device I'm using for the video conference. Context.

Suppose you're on a bus and see a sign that says:

Sign on Bus: No Standing

No standing anywhere in the universe? No, just while on the bus and the bus is moving. Context.

The luxury of communicating within the context of location or conversation is that we can create shorter messages and still convey sufficient meaning for a reasonable person. In writing rules, however, we generally don't have that luxury. So, the relevant context needs to be spelled out in the rules. For example, we can't just write:

Driver Rule: No driving without a license.

How about a fishing license? Would that do? Am I allowed to drive golf balls at the practice range? So, instead we must write:

Revised Driver Rule: Any person operating a motor vehicle on a public roadway must hold a valid driver's license.

Eliminating assumed context is one of the differences between informal communication and formal communication.[1] These differences are well documented by authorities in the field of writing.[2] They actually apply to any kind of formal communication conveying knowledge, not just rules.

Here's another sin of context. In everyday (informal) communication between people, words like 'here', 'now', 'me', 'you', etc. are often taken for granted. Such references are generally easily resolved.

But in writing formal communication, you can never be completely sure who the readers will be, what they know or don't know, and what purpose they may have in reading the material. So, what you write needs to be complete, making no assumptions about context.

Modifiers and Qualifications

Consider the following specifications about whether a customer counts (qualifies) as a gold customer:

Definition of Gold Customer: a customer that regularly places large orders and merits highest-level service

Gold Customer Rule: A customer is considered a gold customer if the customer places more than 12 large orders during a calendar year that are each fully paid within 60 days.

Do you notice there's no clarification of the modifier 'large' in either the definition or the rule above? Currently the question of large-ness (how large is large?) remains a gap in the business logic. Does it need to be closed? If consistent behavior is important, yes.

There are at least three possibilities in this regard, as follows. Your drill-down of the logic is not complete until one of these options (or some other) is selected.

  1. Existing facts (stored data) already indicate whether an order is large (yes/no).

  2. Facts are requested in an interactive dialog with some user(s) during the rule's evaluation.

  3. More rules are written providing criteria for what is meant by 'large'.

In the third case, some additional definitional rule(s) need to be specified, for example:

Large Order Rule: An order is considered a large order if the order nets more than $999.

In rules for business and government, the devil often lies in definitional detail. We call pursuit of that detail "pulling the threads." It's an orderly, gap-closing march toward completeness that requires knowing what questions to ask and how to ask them.

Note that the Large Order Rule actually adds a new term to your business vocabulary, 'large order'. You can use that term in any other rule (in addition to the Gold Customer Rule) without having to respecify the logic. This is an important means by which consistency is achieved across a set of rules.

If you are a close reader, you'll find another gap in the current version of the Gold Customer Rule: What does the qualification "within 60 days" mean? When does the clock start ticking?

  • When the order is received?

  • When the goods are shipped?

  • When the goods arrive?

And when does the clock stop ticking?

  • When payment is received?

  • When the payment is confirmed by the bank?

Qualifications concerning timing like this are quite common in rules. Their logic is not complete until you have explicit criteria for them.

Definitions vs. Definitional Rules

Let's consider the definition of 'gold customer' again:

Definition of Gold Customer: a customer that regularly places large orders and merits highest-level service

You can easily imagine how dense this definition could become if additional logic from the definitional rules discussed above were loaded into it. Machines could probably handle the density; people, not so much. Keep definitions friendly for people by expressing supplemental definitional rules.

Aside: Definitional rules are especially useful where a concept is inherently so mathematical that for practical purposes a definition adds little (e.g., 'average monthly sales'). Consider the concept 'large order'? Does it need an explicit definition in addition to the Large Order Rule? Maybe not. Perhaps that definitional rule is sufficiently clear and complete on its own already.

You might sense I'm saying that definitions should be aimed at basic human communication, whereas definitional rules provide the precision and completeness that machines need. That's only half true — but not the part you might guess. To apply rules consistently, people need precision and completeness too.


[1] Refer to Business Knowledge Messaging: How to Avoid Business Miscommunication, by Ronald G. Ross, (2022).

[2] How Languages Work, by David Crystal, The Overlook Press, Peter Mayer Publishers, Inc., (2005), p. 465.

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Standard citation for this article:

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Ronald G. Ross, "Being Complete in Expressing Rules" Business Rules Journal, Vol. 24, No. 12, (Dec. 2023)

About our Contributor:

Ronald  G. Ross
Ronald G. Ross Co-Founder & Principal, Business Rule Solutions, LLC , Executive Editor, Business Rules Journal and Co-Chair, Building Business Capability (BBC)

Ronald G. Ross is Principal and Co-Founder of Business Rule Solutions, LLC, where he actively develops and applies the BRS Methodology including RuleSpeak®, DecisionSpeak and TableSpeak.

Ron is recognized internationally as the "father of business rules." He is the author of ten professional books including the groundbreaking first book on business rules The Business Rule Book in 1994. His newest are:

Ron serves as Executive Editor of and its flagship publication, Business Rules Journal. He is a sought-after speaker at conferences world-wide. More than 50,000 people have heard him speak; many more have attended his seminars and read his books.

Ron has served as Chair of the annual International Business Rules & Decisions Forum conference since 1997, now part of the Building Business Capability (BBC) conference where he serves as Co-Chair. He was a charter member of the Business Rules Group (BRG) in the 1980s, and an editor of its Business Motivation Model (BMM) standard and the Business Rules Manifesto. He is active in OMG standards development, with core involvement in SBVR.

Ron holds a BA from Rice University and an MS in information science from Illinois Institute of Technology. Find Ron's blog on For more information about Ron visit Tweets: @Ronald_G_Ross

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