We use a standard format for our use cases. Business rules are designed to govern the actions of an event or events, either singly or grouped in a rule base. In some references, nonconditional rules are referred to as business rules. My current project merely calls such rules requirements. We feel the distinction is important because business rule sets can be used within rule engines to process events depending on condition.
Straight requirements act regardless of condition.
Although analogous, this is not the same as the class, responsibility, and collaboration approach. We do not try for class definition in analysis use case development. We save that for design, when architectural dependency issues are more completely specified. Yet, we have used this approach extensively for project management. All of our task statement development and project work breakdown structures are based on the definition of responsibilities and collaborations between project teams where project teams are recognized as actors or classes in the object-oriented sense.