Business rules are of utmost importance to all businesses, but what is a business rule? Many different definitions have been suggested over the past decades (box 1). And for each definition there are even more interpretations. These interpretations vary greatly and are often dependent on how the business rules are managed. Taken together this means that the answer to the proposed question remains ambiguous. In this paper different viewpoints on business rules will be discussed in order to come to an answer to the question: What is a business rule?

Decisions guide business behaviour
Looking at the definitions of a business rule in box 1 it becomes clear that business rules have something to do with decisions. Decisions guide business behaviour [3] and to achieve this influence they must be important for business rules. Because of this paramount role of decisions and their associated rules they are often treated as a synonym for business rules. This is indeed not surprising, as decision rules govern the organisation of knowledge within a business, but can all business rules be expressed in terms of decisions?

Business rules are executable
In many organisations business rules are associated with business rules engines. These engines are software systems that deploy and execute rules in a runtime production environment. In this environment these rules are used to produce information, therefore these rules are called production rules. Decision rules can also be considered a certain kind of production rule, so this viewpoint would also include the important aspect of decision making. The problem with this viewpoint is that not all rules produce information, some rules restrain information to consistent and correct forms.

Business rules ensure integrity
The second definition in box 1 [2] strongly implies that business rules are actually integrity constraints. These rules exist to restrain data to allowed forms and to keep it consistent. This approach claims that a business rule is a business operation reflected in the design of a database. However, as discussed previously, there are more aspects to be considered when looking at business rules.

What is a business rule?
All discussed viewpoints highlight important aspects of business rules, but none providea complete picture. Actually business rules are all of the above and more. Decision rules, production rules and integrity constraints are all business rules. However all these rules would be meaningless if they were not built on a foundation of facts. A vocabulary, consisting of the business terms and facts relating these terms, is necessary to make sense out of the rules. In conclusion business rules consist of an integrated whole of decision rules, production rules and integrity constraints based on a solid foundation of facts.“A rule that is under business jurisdiction”