In our original paper, we defined 'business rule' from the conceptual, information system (I/S) perspective.  We readily acknowledged this narrow focus, which was consciously chosen to let us develop consensus on a set of core concepts.  At the same time, we identified a broader scope for future investigation.  Our current work now focuses on one part of that broader scope ~ on the business perspective of business rules.

Why multiple definitions?  From the I/S perspective, a business rule pertains to the facts of the system that are recorded as data and to the constraints on changes to the values of those facts.  The business perspective of business rules involves the behavior of people in the business (human activity) system.  Because these perspectives are distinct, we have a definition of 'business rule' for each of these perspectives.

From the business perspective,
...a business rule is guidance that there is an obligation concerning conduct, action, practice, or procedure within a particular activity or sphere.

Two important characteristics of a business rule are:

• There ought to be an explicit motivation for it.
• It should have an enforcement regime stating what the consequences would be if the rule were broken.

From the information system perspective,
...a business rule is a statement that defines or constrains some aspect of the business.  It is intended to assert business structure, or to control or influence the behavior of the business.