Business Rules and Business Process Modeling Simplified

In BPMN 2.0 there is a shape for business rules:



 This shape denotes the place within the process model which calls business rules and obtains decision output.  The question is, how do you use it?

The difference between process and rules is simple; processes are stateful and rules are stateless. In BPMN a process has an explicit or implicit single start and one or more stops. In business rules there is no start or stop. It is an expression of a sequence of logical conditions.

Consider the figure below:



Simple Process with exclusive gateway, the process corresponds to the process: Start: When A Condition: Start Activity A When B Condition: start activity B, When either complete: Stop

This simple process uses the exclusive gateway to choose which activity to run. The activity, A or B, will run for an indeterminate time. When it is done the end is reached. A simple flow rule from Visual Rules is shown in Figure 2.  A flow rule is a graphical representation of a path of logic. There is no time element to the evaluation; either condition A or Condition B will be the outcome of the evaluation of the conditions in the two gateways-there is no time element to consider.





Figure 2: Simple decision graph with two exclusive outcomes, the diagram corresponds to the logic IF A condition Then A Outcome else If B Condition then B Outcome.

The two figures compare and contrast the similarities of BPMN and business rules. Both evaluate the logic conditions to decide which process activity or outcome to choose. The contrast is in the time element. This is what we mean when we stay the process is stateful and the decision graph is stateless.

If we connect the flow rule with the process then the process model looks like this:



This is simple, but most process decision are more complicated than that. I discuss process decisions in a white paper located here:

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