Some time ago, I was asked by someone the difference between business rules and requirements. My initial response was to say that business rules are meant to change faster than requirements and that the tools used to manage requirements might not be the best tool to manage rules.

That answer was sufficient at the time but I wanted to refine this answer a little bit and decided to do a little research on the subject and to report my findings here.

An updated answer would now be along these lines:

• Requirements tell you what the application should be doing. It will be using processes and business rules because the combination of all three will give you what you need to know how a business works. These have a tendency to be relatively stable over time for a given system.
• Processes are the steps the business will need to take to achieve a goal. It is supported by decisions which are in business rules. These can change occasionally when there is a need for an updated (or new) process to achieve a goal, or if the goal changes.
• Business rules define the policies that constrain the business (and its processes). Business rules can change independently and much more often than processes and requirements.

In addition to that I would mention that they are all related, but are different enough that the tools to manage each of those are different. Also, separating the business rules out of processes and requirements will position them for change.

The techniques to gather the information on requirements, are also similar although some techniques are better than others at obtaining results^[1].

During my search for more information I found a couple of very interesting articles on the topic.

Live from Business Rules Forum (almost) – Getting It Right. Rules and Requirements in Software by James Taylor

Why Separate Rules from Requirements by Scott Sehlhorst

[1] Elicitation Techniques for Processes, Rules, and Requirements by Scott Sehlhorst