BRManifesto FAQ: Article 4 - Declarative, Not Procedural

   The Business Rules Group
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FAQ re: Principle 4.1
Question: Does principle 4.1 of the Manifesto prohibit use of if-then syntax to express rules?

Rules should be expressed declaratively in natural-language sentences for the business audience.

Syntax of the form "If [condition] then [derived fact]" is acceptable. (So is syntax of the form "[Derived fact] if [condition]".) Syntax of the form "If [condition] then [action]" is not acceptable; it is not declarative. (Also not acceptable is "[Action] if [condition]".)


FAQ re: Principle 4.2
Question: What is the sense of "cannot be expressed" in Manifesto principle 4.2?

If something cannot be expressed, then it is not a rule.

The intended sense is "can't be put into words" or "there's no way to say it". If you can't communicate it, it simply doesn't count.


FAQ re: Principle 4.3
Question: What kind of 'statements' is the Manifesto referring to in principle 4.3?

A set of statements is declarative only if the set has no implicit sequencing.

The Manifesto means any kind of expression, starting with, but not limited to, the statements found in application programs coded in procedural languages.


FAQ re: Principle 4.3
Question: Under principle 4.3 of the Manifesto, when is a set of statements not declarative?

A set of statements is declarative only if the set has no implicit sequencing.

Any set of statements whose evaluation produces a different result when the statements are listed in a different sequence is not a set of declarative rules.


FAQ re: Principle 4.4
Question: Why does Manifesto principle 4.4 maintain that "constructs other than terms and facts imply assumptions about a system implementation"?

Any statements of rules that require constructs other than terms and facts imply assumptions about a system implementation.

Rules expressed purely on the basis of terms and facts (predicates) can be evaluated using formal logic, which assumes no particular kind of system implementation. Any other construct implies bias toward some class of platform or implementation scheme. If rules are shaped by any system concern whatsoever, they are less able to be understood or validated in their right, and less easily redeployed.


FAQ re: Principle 4.5
Question: What is the sense of "enforcement" in Manifesto principle 4.5?

A rule is distinct from any enforcement defined for it. A rule and its enforcement are separate concerns.

The intended sense is "means of ..." or "method of ..." or "approach to ..." enforcement.


References:

[1] The Manifesto is free, only 2 pages long, translated into 15 languages. Have a quick look (or re-look!). No sign up required. Well worth your time.

Standard citation for this article:


citations icon
The Business Rules Group , "BRManifesto FAQ: Article 4 - Declarative, Not Procedural" Business Rules Journal Vol. 3, No. 12, (Dec. 2002)
URL: http://www.brcommunity.com/a2002/s018.html

About our Contributor:


   The Business Rules Group
The Business Rules Group As prepared by members of The Business Rules Group

Originally a project within GUIDE International, the Business Rules Group [BRG] subsequently became an independent organization. BRG's membership comprises experienced practitioners in the field of systems and business analysis methodology. BRG's members are practitioners who work in both the public and the private sectors.

The BRG charter is to formulate statements and supporting standards about the nature and structure of business rules, the relationship of business rules with the way an enterprise is organized, and the relationship of business rules with systems' architectures.

BRG's standards work has been picked up and merged with OMG's.

For more on the BRG visit: http://www.businessrulesgroup.org/theBRG.php

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