The RuleSpeak^® Business Rule Notation

by Ronald G. Ross

In September 2005, the Object Management Group (OMG) approved the "Semantics of Business Vocabulary and Business Rules" (SBVR)[1] to become a final adopted specification of the OMG.  SBVR, which is the first OMG standard for fact models and business rules, is in finalization as of this writing. SBVR is a highly-structured set of fundamental concepts, not a syntax for rule representation.  In part, this approach is necessary for multi-lingual support; in part, it is to ensure support for a variety of representational schemes.  One such scheme is RuleSpeak®, which played a central role in the shaping and proofing of the standard itself.  The material that follows is extracted from the RuleSpeak Annex of SBVR.

RuleSpeak^® is an existing, well-documented^[2] business rule notation developed by Business Rule Solutions, LLC (BRS) that has been used with business people in actual practice in large-scale projects since the second half of the 1990s.  A companion column in this issue of the Journal introduces two styles of business rule statement --   prefixed rule keyword style and embedded (mixfix) rule keyword style.  That article details a business rule notation within SBVR Structured English that features prefixing rule keywords onto appropriate propositions.^[3]    RuleSpeak can also use the constructs of SBVR Structured English, but embeds equivalent keywords within the propositions themselves (mixfix).

As that article explains, more than one notation for expressing business rules is possible using SBVR Structured English.  (This is probably also true for other notations compliant with SBVR.)  Regardless of how expressed, equivalent semantics can be captured^[4] and formally represented as logical formulations.

Expressions in RuleSpeak

RuleSpeak builds on the same expression forms described in the SBVR Structured English Annex of SBVR (Annex C), with the minor difference that distinct keywords are used for the Modal Operations related to business rules.  The following section presents the RuleSpeak alternative rule keywords for Rules and Affirmations and Admonitions.^[5]

Modal Operations in RuleSpeak

Modality claim type	Statement form	SBVR Structured English keywords	RuleSpeak keywords
obligation claim	'obligative statement' form	it is obligatory that p	r must s
obligation claim embedding a logical negation	'prohibitive statement' form	it is prohibited that p	r must not s
	'restricted permission statement' form	it is permitted that p only if q	r may s only t
permissibility claim	'unrestricted permission statement' form	it is permitted that p	r may s
			r need not s

necessity claim	'necessity statement' form	it is necessary that p	r always s
necessity claim embedding a logical negation	'impossibility statement' form	it is impossible that p	r never s
	'restricted possibility statement' form	it is possible that p only if q	r can s only t
possibility claim	'unrestricted possibility statement' form	it is possible that p	r sometimes s
			r can s

Notes:

• p and q, and r, s, and t, are all parts of the same proposition, say u.

• In a permissibility claim or a possibility claim, the 'only' is always followed immediately by one of the following:
  1. an 'if' (yielding 'only if').
  2. a preposition.

An example of a business rule statement using the 'only [preposition]' form is the following:

A spot discount for a rental may be given only by a branch manager.

Example in RuleSpeak

Each rental car must be owned by exactly one branch.

The example above includes three keywords or phrases, two terms (designations for noun concepts), and one fact type symbol (designation for a fact type), as illustrated below.

As noted above, every Operative Business Rule or Affirmation or Admonition can be stated by using one of the following embedded keywords.

must	or  should	rule keyword
must not	or  should not	rule keyword
only	often as in  only if	rule keyword
may	or  need not	affirmation / admonition keyword

Every Structural Rule or Affirmation or Admonition can be stated by using one of the following embedded keywords.

always		rule keyword
never		rule keyword
can ... only	often as in  can ... only if	rule keyword
sometimes	or  not always or  can	affirmation / admonition keyword

Special-purpose keywords for indicating specific kinds of Structural Rules include the following.  In these forms, 'always' is assumed implicit.

is to be considered		for derivation or inference
is to be computed as		for computation
is to be fixed at [number]	or is to be [number]	for establishing constants

Among the most basic usage rules and guidelines of RuleSpeak are the following.  (Note that these usage rules and affirmations/admonitions are given using proper RuleSpeak notation.)

1.	'Should' may be used in place of 'must' in expressing a business rule only if one of the following is true: The business rule does not have an enforcement level. The business rule has an enforcement level, and that enforcement level is consistent with the English sense of 'should'. Comment:  To say this differently:       'Should' must not be used in place of 'must' in expressing a business rule if all of the following are true: The business rule has an enforcement level. The enforcement level of the business rule is inconsistent with the English sense of 'should'.
2.	'May' must be used in the sense of 'permitted to' in RuleSpeak.  'May' must not be used in the sense of 'might'.[6]
3.	An affirmation or admonition must not include a rule keyword.
4.	A statement expressing a rule or affirmation or admonition should not begin with a condition.   Comment:  'Condition' as used here means a qualification set off by 'if', 'while', 'when', etc.  (e.g., 'If a rental is open....').
5.	A double negative should be avoided in expressing a rule in RuleSpeak.   Comment:  Double negatives, especially using two 'not's, are generally undesirable in good English usage, and often prove particularly troublesome in rule statements.   Example:   Rule:  A withdrawal from an account must not be made if the account is not active.   Revised rule:  A withdrawal from an account may be made only if the account is active.   Comment:  The revised rule is expressed in the form of a 'restricted permissive statement'.

References

[1]  Semantics of Business Vocabulary and Business Rules (SBVR).  First Interim Specification, March 2006.  Available as dtc/06-03-02 at http://www.omg.org 

[2]  Ronald G. Ross.  Principles of the Business Rule Approach.  Boston, MA:  Addison-Wesley, 2003, Chapters 8-12.  Versions of RuleSpeak have been available on the Business Rule Solutions, LLC website (www.BRSolutions.com) since the late 1990s.  Public seminars have taught the syntax to thousands of professionals starting in 1996 (www.AttainingEdge.com).  The original research commenced in 1985, and was published in The Business Rule Book, 1994 (www.BRSolutions.com).

[3]  SBVR Excerpt, "Notations for Business Rule Expression," Business Rules Journal, Vol. 7, No. 4 (Apr.. 2006), URL:  http://www.BRCommunity.com/a2006/b286.html

[4]  For a business-oriented, SBVR-compliant approach, see:  Ronald G. Ross.  Business Rule Concepts:  Getting to the Point of Knowledge.  2nd ed.:  Business Rule Solutions, LLC, 2005, Chapters 4-5 (www.BRSolutions.com).

[5]  It is important to note that use of these keywords must be in a context that is clearly indicated to be for Rules and Affirmations/Admonitions only.

[6]  Principles of the Business Rule Approach, p. 130.

standard citation for this article: Ronald G. Ross, "The RuleSpeak® Business Rule Notation," Business Rules Journal, Vol. 7, No. 4 (Apr. 2006), URL:  http://www.BRCommunity.com/a2006/b282.html