Excerpted from Chapter 3, Business Rule Concepts:  Getting to the Point of Knowledge (Third Edition), by Ronald G. Ross (August 2009). ISBN 0-941049-07-8   http://www.brsolutions.com/publications.php

Any discussion of business rules would not be complete without considering exceptions.  To do the topic justice, however, requires a bit of groundwork.  Let's examine the following two warehouse business rules:

Business Rule 1:  A gold customer must be allowed access to the warehouse.

Business Rule 2:  A customer may have access to the warehouse only during regular business hours.

Suppose some gold customer seeks access after regular business hours.  Under that potential scenario we have a conflict.

A basic SBVR^[1] principle for business rules is that any guidance statement whose meaning conflicts with some other guidance statement(s) (or even some other part of the same statement) must be taken that way.  In other words, if by taking some expression(s) literally you find that a potential conflict could arise, you are right — it can.  You need to fix it.  The principle is really about being able to fully trust what you read in front of you.  If statements of business rules don't mean literally what they say, then can you really ever be sure what they do say!?

So guidance statements should always be taken to mean exactly what they actually say — no more, no less.  Potential conflicts such as the above must be resolved explicitly, within the actual statement(s).  Several approaches that don't work in that regard include:

• Setting up some priority scheme to determine which 'wins'.
• Expressing some separate business rule(s) to determine which 'wins'.
• Deferring to some level of categorization to determine which 'wins' (e.g., A gold customer is a category of customer; therefore 'customer' rules 'win' over 'gold customer' rules).

To apply each business rule correctly under any of these approaches, sometimes you need to know more than just what a statement says.  In other words, sometimes semantics are hidden or, at least, external.  Not good.

The only viable solution is that once a potential conflict is discovered, the guidance statement(s) that produce(s) that conflict need to be restated to avoid it.  In other words, the statement(s) must accommodate the problematic circumstances.  This guiding principle — the correct one for business communication — is called Accommodation.

So one of the warehouse business rules needs to be re-written.  Which one?  The answer depends entirely on business practice.  Which of the following reworded versions might represent the correct or desired business practice?

Reworded Business Rule 1:  A customer must be given access to the warehouse if the customer is a gold customer and the access is during business hours.

Reworded Business Rule 2:  A customer that is not a gold customer may have access to the warehouse only during business hours.

Let's say the desired business practice is given by the second statement.  So the two business rules jointly representing the correct business practices for warehouse access are:

Business Rule 1:  A gold customer must be allowed access to the warehouse.

Business Rule 2:  A customer that is not a gold customer may have access to the warehouse only during business hours.

Now we can finally address the issue of exceptions.  Looking at the two resulting warehouse-access business rules ask yourself:  Which is an exception?!  Both?  Neither?  The formal answer is, once you accommodate, there really are no exceptions(!).  There are just well-stated, fully-trustworthy business rules.

In conversation and other informal business communication, we often do talk about "exceptions" to business rules.  For example we might say:  A customer may have access to the warehouse only during regular business hours.  Then later in the same conversation or message we might add:  By the way, none of what I've said applies to gold customers.

Statements of business rules, however, should not be informal in that sense.  You can never be sure when or where a statement might be read or what the context might be.  So a business rule statement needs to express its full meaning.  David Crystal, a noted world authority on language, explains things this way:^[2]

"When someone consults a reference book … [in which] information is stored for future use, it is impossible to predict who is likely to use it … There is no 'dialogue' element in the communication.  The information has to be as self-contained as possible, for it is impossible to predict the demands which may one day be made on it, and in most cases there is no way in which the user can respond so as to influence the writer.  Accordingly, when language is used for [such] purposes … it is very different from that used in everyday conversation — in particular, it displays a much greater degree of organization, impersonality, and explicitness."

Now, I've never met or talked to David Crystal, but I'm confident I get his meaning.

This principle of expressing the full meaning of each business rule is called Wholeness.  Suppose your rulebook is deemed free of conflicts and you understand the business vocabulary correctly (two big if's of course).  If your guidance statements are all expressed wholly, then:

• Every statement is always self-explanatory.  No need to appeal to any other statement should ever arise in understanding the full meaning.
  
  
• Every statement can always be taken at face value.  Take it out of conversational context and you can still trust exactly what it says.

By the way, there's a great deal a general rulebook system (GRBS) could do to simplify and condense whole statements for easier consumption — if it knew each worker's preferred conversational context.  That would give you friendly and formal business communication.

References

[1]  Semantics of Business Vocabularies and Business Rules (SBVR) is a groundbreaking standard officially released in December, 2007 by the Object Management Group (OMG).  For background on SBVR, refer to Ronald G. Ross, "The Emergence of SBVR and the True Meaning of 'Semantics':  Why You Should Care (a Lot!) ~ Part 1," Business Rules Journal, Vol. 9, No. 3 (March 2008).  Available at:  http://www.BRCommunity.com/a2008/b401.html

[2]  David Crystal, How Languages Work, Woodstock, NY, The Overlook Press, Peter Mayer Publishers, Inc. (2007), p. 465.

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