What is a bi-directional business rule?

Question

Does the following fit the definition of a bi-directional business rule?

1. An employee of the car rental company handles the client but each client can only be handled by one employee.

Answer 1

Directionality is often important to consider in UML and database modeling contexts. These models are then used as the base models for business rule systems. In the context of business rules, directionality allows you to navigate from some some object to another object that it nows about. So in your example you could start with the employee and write some rule about the client:

if the client of the employee is a relative of the employee then raise an audit exception.

Here you started with the employee and navigated to the client with the "of the" phrase.

The reverse navigation might be:

if the employee serving the client is a relative of the client then raise an audit exception

So here you have bi-directional navigation while authoring the business rules. This might be important and provide some value to the rule authors so that they can start their authoring with either the employee or the client, or it might not. That is a decision you would have to make while designing the rule authoring language.

Another possibility is that you are actually expressing the cardinality of the relationships that are possible in the base model by using rules. But this is not a frequent use case. If you think about it, this kind of cardinality expression is not likely to change much and probably shouldn't be handled at the business rule level. For example, do you need to give the business rule authors the ability to express and change the fact that an employee can only handle one client versus some point in the future where they can handle 1 .. N clients? That might make sense in a non-operational decision model, but will not likely come into play with operational business rule systems.