Premise and Conclusion

RuleSpeak^® Sentence Forms
Specifying Natural-Language Business Rules in English

by Ronald G. Ross

For a free download of the RuleSpeak Sentence Forms, complete with examples and list of do's and don'ts in expressing Business Rules, visit www.RuleSpeak.com.  Also available for free in Dutch, German, and Spanish.

What is a Sentence Form?

Definition and Purpose

A Sentence Form is a basic pattern or template in natural language that can be used to express a certain kind of Business Rule in a consistent, well-organized manner.  Each Sentence Form is aimed for a particular kind of guidance.

The purpose of the RuleSpeak^[1] Sentence Forms is to ensure that written Business Rules are more easily understood.  They also help ensure that different practitioners working on a large set of Business Rules express the same ideas in the same way.  Such consistency would not be possible if Business Rules were expressed in a completely "free-form" manner.

The Sentence Forms are not technical in nature.  In other words, they do not represent a formal language or syntax for implementing Business Rules using a software platform (e.g., a rule engine).  Rather, they are aimed at expressing Business Rules to improve communication at the business level.

Success Factors for the Sentence Forms

What is important — and what is not important — when applying the RuleSpeak Sentence Forms?  One thing that should not be considered is how the Business Rules will actually be implemented using a particular rule engine or programming language.  What matters above all else is effective business communication.  Sticking to that perspective sometimes proves difficult for those responsible for technical implementation.  They may want to get to the IT versions directly.  But doing that will not help with capturing the Business Rules succinctly from the business perspective.

Using the Sentence Forms to express Business Rules does require a modest measure of discipline.  This discipline can be achieved through a bit of practice, and by understanding certain fundamentals.  These fundamentals are discussed later in this column.

Finally, it is important to understand the level of Business Rules to which the Sentence Forms should be applied.  As above, the Sentence Forms are not aimed at system design or automation.  They are also not aimed at the highest forms of guidance — that is, the language of laws, regulations, contracts, business policies, etc.

Rather, the Sentence Forms are aimed at what is called practicable guidance.  Practicable Business Rules are ones used to make operational business decisions on a day-in-and-day-out basis.  If a business worker is properly authorized, and understands the business vocabulary, he or she should be able to apply the practicable Business Rules directly in the conduct of on-going business activity.

Often, these practicable Business Rules must be interpreted from the higher forms of guidance in order to clarify, disambiguate, and solidify their business intent.  The Sentence Forms facilitate such interpretation by providing predictable patterns of expression.  The same is true if practicable Business Rules are being reversed-engineered bottom-up from existing implementations or documentation, or harvested on a facilitated basis from subject matter experts.

Usage Notes

• "Shall" – Highest forms of guidance — laws, regulations, contracts, business policies, etc. — often use the word "shall".  We prefer the less formal word "must", which is generally more appropriate for practicable Business Rules.
  
  
• "Should" – Any Business Rule can be stated using "should" instead of "must".  Using "should", however, reflects an assumption or decision about the appropriate enforcement level of a Business Rule.  We prefer to document any sense of how strictly a Business Rule is to be enforced separately from the expression of the Business Rule itself.  We therefore prefer always using the word "must" instead of "should".
  
  
• "May" – We always use the word "may" in the sense of something being allowed (or disallowed).  We never use "may" in the sense of "might" — i.e., that something might occur or might be true.  Unfortunately, "may" does have this double usage in English, but no suitable alternative exists.  In any event, experience has proven that the correct sense "is allowed" quickly wins out.

Basic Concepts

Understanding fundamental ideas about expressing Business Rules will assist greatly in writing them effectively.  Briefly, these ideas are as follows.

Every Business Rule Statement should use a Rule Keyword

Every Business Rule can be expressed using one of the following two words.

• "must"
• "only"

These fundamental words are called the RuleSpeak Rule Keywords.  It is very important that every Business Rule Statement include exactly one of these two Rule Keywords.

Practicable guidance comes in two varieties

A Business Rule always removes a degree of freedom.  The presence of one of the two Rule Keywords in a sentence clearly indicates that intent.

A large majority of sentences typically expressed to give guidance are Business Rule Statements.  Sometimes, however, practicable guidance is worth expressing that does not remove a degree of freedom.  Such a Statement, which simply clarifies that something is allowed, or that something is not required, is called a Statement of Advice.

A Statement of Advice should never include either of the two Rule Keywords.  Instead, it should use exactly one of the following two RuleSpeak Advice Keywords.

• "may"
• "need not"

Note that "may" coupled with "only" in the same sentence always produces a Business Rule, not an Advice.  Statements of Advice and Business Rule Statements are both Guidance Statements.

Every Guidance Statement should be a complete sentence

English helps ensure wonderful completeness in the communication of thoughts (propositions) through grammatical rules about forming sentences.  Follow those rules religiously in writing all Guidance Statements.

Every Guidance Statement should have a subject

In good English construction, every sentence has a subject.  Although this subject may be implied or the sentence inverted, more often than not an explicit subject appears as the first word or phrase in the main body of the sentence.  Such sentences are usually direct and, if well written, easy to follow.  (The subject in the previous sentence, for example, is "sentences".)

RuleSpeak prescribes that Guidance Statements have an explicit subject at the beginning.  This subject should be a noun, possibly qualified.  The singular form is preferred.  This approach promotes overall clarity and consistency.

Many IT notations feature "If … then…" syntax for implementing Business Rules in rule engines or programming languages.  In such notations, the true subject does not appear until after the 'if' clause.

Besides being 'unfriendly' for business communication, such syntax is problematic for expressing certain types of guidance.  What, for example, is the "if" of the Business Rule Statement, "An employee must have a name."?

Any Guidance Statement may reference an instance

An instance is a single thing, rather than a class of things.  Instances can be referenced by Guidance Statements just as can classes of things.  If there could be any doubt as to whether a term in a Guidance Statement refers to an instance or a class, the prudent approach is to put the term in single quotes.

Example:  A yearly personal U.S. tax return is due on April 15.

In this example, there is only one "April 15" on a calendar, so there is little chance of confusion.  Similarly, there is only one country "U.S.", so this reference too is probably clear.

Example:  A 'flammable' sticker must be displayed on a tank containing a combustible fuel.

In this example, "flammable" refers to an instance of the class of things "sticker", rather than to a kind or category of sticker (i.e., a sticker that is flammable).  Therefore the word "flammable" has been enclosed in single quotes.

Qualifying Guidance Statements

Most Guidance Statements include some qualification(s) indicating the circumstances under which they apply.  Often but by no means always such qualification is expressed using "if".

Example:  A shipment must be insured if the value of the shipment is greater than $500.

Many qualifications can be expressed without using "if".

Example:  A retired employee must not be assigned to a project.

Here the qualification "retired" is used to modify "employee" directly.  This natural means of qualification is perfectly acceptable.

Example:  A shipment fee may be waived only for an order placed by an in-state customer.

Here the qualification "placed by an in-state customer" modifies "order" in a natural manner.  It too is acceptable.

Guidance that applies only at some point(s) in time

The word "if" indicates that qualification is continuous over time.  The word "when" should be used if a Guidance Statement applies only at certain point(s) in time.

Example:  The total enrollment fee amount owed by a student for a semester must be $5,065 when the student registers for that semester.

As stated, this Business Rule applies only at each point in time when a student registers for some semester.  At any other time, the Business Rule is assumed not to apply; that is, the total enrollment fee amount owed for the semester does not have to be $5,065 (and probably increases!).

Allowing something conditionally

The Sentence Form "… may … if …" (without an "only") should always be avoided.  Statements using that Sentence Form are quite tricky and can be easily misunderstood.

Example:  An item may be returned if some proof of purchase is provided.

This Statement expresses an Advice.  (This interpretation is dictated by logic.)  It covers only the situation in which some proof of purchase is provided.  It literally does not say anything about whether an item may be returned if some proof of purchase is not provided.  Most likely, however, the business intent was to disallow returns without providing some proof of purchase.  Assuming that to be the case, the Rule Keyword "only" should be inserted as follows, thereby turning the Advice into a Business Rule.

Example:  An item may be returned only if some proof of purchase is provided.

Qualifications in Statements of Advice based on the Sentence Form "… may …" expressed without using "if" are not as easily misunderstood.  They are therefore acceptable if used carefully.

Example:  A retired employee may work part-time in Alberta.

This Statement must be taken to express an Advice.  It does not imply anything about employees who are not retired, not working part-time, or not working in Alberta.  It just says what it says.  If some Business Rule is intended covering some or all of these circumstances, it must be expressed separately, as the following Business Rule Statement illustrates.

Example:  A retired employee must not work part-time outside Alberta.

How to say something is not a Business Rule under certain circumstances

If something is not a Business Rule under certain circumstances, the best Sentence Form to express the Advice is generally " … need not … if …".

Example:  A credit check need not be requested for an order if the amount of the order is under $1,000.

References

[1]  RuleSpeak was one of three reference notations used in the creation of SBVR (Semantics of Business Vocabulary and Business Rules) and is consistent with that standard.  RuleSpeak is a technique of Proteus^® — the BRS methodology for business analysis and business rules.  RuleSpeak^® is a registered trademark of Business Rule Solutions, LLC.  Read more about RuleSpeak on www.RuleSpeak.com.

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Provided courtesy of Business Rule Solutions, LLC, the Business Rule Technique Company.