In January 2008, the "Semantics of Business Vocabulary and Business Rules" (SBVR) was first presented by the Object Management Group (OMG) as an official specification of the OMG.  Version 4 (SBVR 1.4) was published in 2017.[1]

The first three instalments of this series provided a basic context for understanding the "Semantics of Business Vocabulary and Business Rules" (SBVR).  We began with an examination of each of the elements of the title:  Semantics, Business Vocabulary, and Business Rules.  Next, we moved to look at five major aspects of SBVR:  community, shared meanings, logical formulation, and business representation, with a grounding in formal logic.  And last time, we explored how SBVR supports the business rules approach, illustrating how SBVR aligns with notions of the Business Rules 'Mantra' (rules, facts, terms/concepts).  In this article we dive into the heart of SBVR — the business-facing vocabularies and, in particular, the vocabulary for business rules.

SBVR is itself presented as a vocabulary, or actually a set of sub-vocabularies (clauses of the SBVR document), each containing a set of terminological entries.  One collection of these sub-vocabularies is considered the Vocabulary for Describing Business Rules.  This article provides an introduction to that vocabulary, as extracts from its key entries along with concept model diagrams^[3] that provide a visual picture of relevant sections of the vocabulary.

As we learned last time, in SBVR the meanings of rules and concepts are modeled separately from how they are expressed.  Accordingly, the concepts in the Business Rules Vocabulary belong to one of two main groupings:  the first is for the concepts of business rules ("Figure 1. Categories of Guidance"); the second is for statements used to express business rules ("Figure 2. Statements of Guidance").^[4]

Categories of Guidance

Figure 1.  Key Categories of Guidance

element of guidance

The highest-level concept in the taxonomy of business rules meaning is 'element of guidance', which is a category of 'proposition'.^[5]  An element of guidance is a means^[6]  that guides, defines, or constrains some aspect of an enterprise.  An element of guidance is intended to assert business structure or to control or influence the behavior of the enterprise. 

A key notion of 'element of guidance' is that its formulation is under the enterprise's control by a party authorized to manage, control, or regulate an enterprise, selecting from alternatives in response to a combination of assessments.  Two important kinds of 'element of guidance' are business policy and business rule.^[7]

business policy

A business policy is an element of guidance that is not practicable^[8] whose purpose is to guide an enterprise.  Compared to a business rule, a business policy tends to be less structured, less discrete or not atomic, and less carefully expressed in terms of standard vocabulary — not directly enforceable — (in addition to being not practicable).

business rule

In contrast to a business policy, a business rule is practicable.  While the two are distinct, business policy and business rules may be related; business policy can be the basis for business rules.

A business rule is a rule that is under business jurisdiction — with rule being a kind of proposition (a claim of obligation or of necessity).  Business rules are based on verb concepts, meaning that the business rules are formulated using verb concepts.

A business rule is either a behavioral (operative) business rule or a definitional (structural) business rule.

behavioral business rule

A behavioral business rule is a business rule that covers conduct, action, practice, or procedure within a particular activity or sphere.  More formally, a behavioral business rule is a business rule that is a claim of obligation, i.e., that there is some obligation concerning conduct, action, practice, or procedure.  We will take a closer look at some behavioral business rules in a future article; meanwhile, it may help to think of a behavioral business rule simply as a business rule that is intended to shape the behavior of people — even when that behavior is automated.

definitional business rule

A definitional business rule is a business rule that is a claim of necessity.  We will take a closer look at some definitional business rules in a future article; meanwhile, it may help to think of a definitional rule informally as a business rule that is intended as some 'definitional criterion'.

enforcement level

An important distinction between definitional business rules and behavioral business rules is that definitional rules (known in formal logics as 'alethic rules' or 'logical necessities') cannot be violated — they are simply true by definition.  In contrast, behavioral business rules (known in formal logics as 'deontic rules' or rules about 'duty') are obligations that can be violated.  Accordingly, a behavioral business rule can therefore have an 'enforcement level'.

SBVR defines enforcement level as something that represents a position in a graded or ordered scale of values that specifies the severity of action imposed in order to put or keep a behavioral business rule in force.  While SBVR does not prescribe any particular scheme of 'enforcement level' values, it does provide an example set.^[9]

Statements of Guidance

Figure 2.  Key Categories of Statements of Guidance

As Figure 2 shows, the top part of the taxonomy on the expression side of the concept model closely mirrors that on the meaning side.  Each of the two forms of statement (behavioral business rule statement and definitional rule statement) is specified as expressing its corresponding meaning-side element: 

Each behavioral business rule statement expresses exactly one behavioral business rule.

Each definitional rule statement expresses exactly one definitional rule.

The converse, of course, does not have this restriction since a given business rule can be expressed in many different ways.

Categories of Behavioral Business Rule Statement

Each of these two kinds of business rule statement itself has categories for its own various kinds of statement forms, as follows.^[10]

obligation statement

An obligation statement is a behavioral business rule statement that is worded as some given state of affairs being obligated.  For example, 

It is obligatory that a rental incurs a location penalty charge if the drop-off location of the rental is not the EU-Rent site of the return branch of the rental.

prohibition statement

A prohibition statement is a behavioral business rule statement that is worded as some given state of affairs being prohibited.  For example, 

An open rental must not have an intoxicated driver.

restricted permission statement

A restricted permission statement is a behavioral business rule statement that is worded as some given state of affairs being permitted only if a given condition is met.  For example, 

It is permitted that a rental is open only if an estimated rental charge is provisionally charged to the credit card of the renter of the rental.

Categories of Definitional Rule Statement

necessity statement

A necessity statement is a definitional rule statement that is worded as some given state of affairs being necessary or being always the case.  For example,

It is necessary that each rental has exactly one requested start date.

Each rental always has exactly one requested car group.

impossibility statement

An impossibility statement is a definitional rule statement that is worded as some given state of affairs being impossible or being never the case.  For example, 

The pick-up branch of a one-way rental is never the return branch of that rental.

The same rental car is never owned by more than one branch.

restricted possibility statement

A restricted possibility statement is a definitional rule statement that is worded as some given state of affairs being possible only if a given condition is met or being possibly the case only if a given condition is met.  For example, 

A rental can be an open rental only if the rental car of the rental has been picked up.

Next time...

As the examples above illustrate, there is some variety in the language styles used in business rule expression.  In fact, for any of the categories above, multiple expression styles can be used.  For instance, the last rule statement example above ("A rental can be an open rental only if the rental car of the rental has been picked up.") could just as well be stated as "It is possible that a rental is an open rental only if the rental car of the rental has been picked up."  While the normative coverage of SBVR does not extend to the language or notation used to express an SBVR vocabulary+rules, SBVR does document three notations.  Next time, we will look at business rule expression forms in more detail.

References

[1]  Semantics of Business Vocabulary and Business Rules (SBVR).  Object Management Group.  The current version of SBVR is available on the OMG site.  

[2]  Quick Reference for Basic SBVR Terminology (v. 4)

[3]  The purpose of the concept model diagrams in the normative sections of SBVR is to display elements of the vocabulary graphically.  SBVR Annex C provides an explanation of the use of UML notation in a business context to represent an SBVR-style vocabulary as a concept model diagram.  Note that these diagrams are not diagrams of the MOF metamodel that is generated from a vocabulary, and these two uses of UML should not be confused.  

[4]  The SBVR Business Rules Vocabulary is defined in Clauses 16 through 18 of the SBVR document.  Only the core concepts are summarized here.  If you are interested in exploring some of the other fundamental principles for business rules, you are encouraged to take a look at Clauses 16 through 18.  

[5]  'Proposition' is explained in SBVR as:  meaning that is asserted when a sentence is uttered or inscribed and which is true or false.  

[6]  This sense of 'means' (the noun, as in 'ends and means', rather than the verb 'is meant as') arises from the Business Motivation Model.  (See:  The Business Rules Group, The Business Motivation Model:  Business Governance in a Volatile World, release 1.4 (May 2010).  Available at  www.BusinessRulesGroup.org and now an OMG-adopted standard.)  

[7]  There is a third kind of element of guidance — 'advice' — which we will explore in a later article.  

[8]  The more complete SBVR definition of 'business policy' gets into aspects of governance.  For our introductory look, the key trait of being 'practicable' (or not) serves to explain how policy and rules are distinguished.  'Practicable' means that a person who knows about the element of guidance could observe a relevant situation (including his or her own behavior) and decide directly whether or not the business was complying with the element of guidance.  

[9]  The example set is taken from the Business Motivation Model.  And for another discussion of 'enforcement level' see:  Ronald G. Ross, "How Rules and Processes Relate — Part 6.  Point-of-Knowledge Architecture (POKA)," Business Rules Journal, Vol. 7, No. 3 (Mar. 2006), URL:  http://www.BRCommunity.com/a2006/b276.html  

[10]  The examples are drawn from the familiar EU-Rent example, which is detailed in a separately-packaged annex of SBVR.  

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