Artifact: Business Rules
This artifact expresses policies and constraints that apply to the business.
Domains: Business Modeling
Purpose
Business rules are intended to assert the desired structure of the business or to control or influence the behavior of the business.  They capture policies and constraints expressed by the business that need to be challenged and/or accepted as requirements.
Relationships
Description
Main Description

A business rule defines a specific constraint or invariant that must be satisfied by the business. Business rules may apply always (in which case they are called invariants) or only under a specific condition. If the condition occurs, the rule becomes valid, and must therefore be complied with. 


Note that a business rule is declarative, not procedural. It describes a desirable, possible state that is suggested, required or prohibited. It may be conditional, that is, if something is the case, something else must or must not be the case. It does not, however, describe the steps to be taken to achieve the transition from one state to another, or the steps to be taken to prohibit a transition. [BRG 2000 - Business Rule Group "Defining Business Rules ~ What Are They Really?" Revision 1.3 July 2000]


A business rule may provide a set of conditions that govern business behavior or provide the criteria for when an action is successfully or unsuccessfully completed. It may stipulate what other actions can or cannot be performed as a result of successful or unsuccessful completion. It may specify the response to some external event that impinges on the enterprise. It may govern relationships that need to apply among various business entities.

Tailoring
Impact of not having

If business rules are not documented, business people cannot validate them. If they are not identified as requirements, developers may have to perform the analysis in order to understand them or they may instead build a solution that does not comply with business rules. The rules are then likely to be represented directly in design artifacts such as code and data structures. This makes them difficult to find and change when the business wants to adapt and change. The resulting inflexibility has a direct business effect on business flexibility.


Also, if Business Rules are not brought together in a single artifact, there will be no opportunity for identifying rules that can be reused in different parts of the system or business. If reuse is not identified it is possible that rules will be implemented that are inconsistent with other rules.

Reasons for not needing

This artifact may not be needed if there is already a Business Rules artifact that can be referenced or extended. If there are no Business Rules, then the artifact is not required.

Representation Options

Business rules can be documented in a structured format as a text document or included as part of a model either as structured text or using a more formal notation such as OCL. The benefits of formally modeling these in one or more tools is that they are directly implementable with their related models, however this has the drawback that they cannot be easily reviewed as a single set of rules.  It is for this reason that it is sometimes better to just use structured text, which can either be maintained as part of a model for better traceability and structuring, or maintained as a separate document that is referenced from the model which provides the convenience of a single source. The various design models must then be validated against this single rules set to ensure that they appropriately implement the rules as stated.

Structured text
A term used to describe text that employs a variety of methods of presentation, such as tables and diagrams, instead of sentences and paragraphs.

UML Representation: Constraint, stereotyped <<business rule>>.

Selected Representation:

Business Rules should be recorded with some level of formality. Different subject areas such as data rules, task flow rules or legal and regulatory rules require different styles and levels of formalism. It is therefore not possible to recommend a single selected representation. The Business Rules checklist and guidance should be consulted for appropriate guidance.