The level of specificity between policy and business rule strikes me as somewhat similar to the relationship between high level requirements and detailed requirements.
Point #3 – Behaviour-related business rules
Business rules fall into one of two categories – behavioural and definitional. Behavioural business rules are intended to affect people’s conduct or actions. The idea is either to get a person to do something or prevent him/her from doing something. The hardhat example above is an example of a behavioural business rule worded to get people to do something (i.e. put on a hardhat). Funnily enough the same rule could be worded from a preventing perspective - “No admittance to this site without a hardhat.”
Advice is another concept in the world of business rules. Rather than restricting, advices are the business expressing explicitly what is permitted or not restricted. “No smoking, except in designated areas” is a behavioural business rule restricting people from smoking in undesignated areas belonging to the business. “Smoking permitted in this area” advises that people who want to smoke, can within the posted area.
Point #4 – Definitional business rules
Behavioural business rules are established by a business to get people to act in specific ways. Those rules ideally will be followed, but may not be by everyone, all of the time. Definitional business rules establish what is ‘true’ within the context of that business and remains true for the business as long as the rule stands.
The following examples are definitional business rules within the context of a car rental company:
Example 1 – A Driver is a person that has proof of a valid driver’s licence.
This rule ‘defines’ the concept driver within the context of this business. If this were a golfing business the term would likely have a very different definition. The trick with defining one term is that the other words/terms used in the definition need to be ones that are understandable to business people.
Example 2 - A rental agreement is not complete without identifying at least one driver.
This rule is about one specific status value of a rental agreement. Similarly to how behavioural business rules can be about preventing rather than doing, there can be definitional business rules about what is not true. That is the case here. The rule is stating that the status cannot have the value ‘complete’ under conditions defined in the rule.
Example 3 - A rental spanning seven or more days qualifies for weekly rates.
The third rule defines the conditions under which it is valid to utilise a particular set of rates. The specific rate value from within the set that applies cannot be determined from this one rule. There must be other rules defined that would work in conjunction with this one for identifying one specific rate that is applicable under those combined conditions.
As stated above, definitional business rules state what is or should be true within the context of this business (or what is not true within the context of the business). As the business operates there can be cases where what the rule states is not as it should be. For example, a person renting a car using a forged driver’s licence. While this violates the rule it does not change the definition of what a driver is for that business. Similarly, a rental agent might let a customer have a weekly rate on a rental of less than seven days, but that does not change the rule / definition of what it takes to qualify for that rate. Definitional business rules are what the business intends to be ‘always true’.
Point #5 – Context is everything (and language is a bitch)
We saw above that the term driver had one meaning in the context of car rental and another one in the context of golf. The good news is that the context of business rules is always the business or organisation managing its rules. The bad news is that one term does not equal one business rule. As seen in the examples ‘stating’ a business rule involves one or more sentences, those sentences containing a number of nouns and verbs in whatever language is being used (e.g. English). But that’s not all. Sentences, in addition to nouns and verbs utilise a number of qualifier words such as must, greater than, not and many more.
The objective of business rules is to get consistent behaviour or results. That involves consistent understanding of the terms used to express the rules, with sentences constructed in a way that the combination of terms is understandable to all involved.
Business rules – seriously?
Show of hands – who thought the three example business rules presented in Point #4 were ‘well-defined’ business rules? Prior to undertaking this article my hand would have been raised. But having ‘looked under the hood’ at what serious business rule people do, I know a lot more about how much I don’t know. Ideally the take away points from Keri’s presentation will have raised your awareness about business rules and the complexities of defining them well. For those of you that seek more on this subject there is a document Keri was involved with titled Semantics of Business Vocabulary and Business Rules (SBVR). It includes a meta-model of rule-related concepts and a case study showing many good examples of well-defined behavioural and definitional business rules. The document is downloadable at http://www.omg.org/spec/SBVR/1.0/PDF.
Where to from here? Personally I do most of my business analysis at the IT Project level. Serious business rule analysis is supposed to take place at the business level, independent of any IT projects or solutions. When necessary I will use those existing templates and do my best to represent business rules within the context of the project, incorporating what I learnt from Keri’s slides and numerous emails exchanged with her while drafting this article – thanks again Keri!
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