Modeling Decisions

Business processes usually contain multiple process branches: Processes branch off and are merged again. Different paths are possible: Process branches may run parallel and are processed independently of each other, or their progress may depend on the occurrence of predefined conditions.

With BPMN, gateways are used to split the process flow into two or more branches. Depending on the used gateway element...

• ...the branches are determined by defined conditions (exclusive gateway)

• ...the branches run in parallel (parallel gateway).

Gateways split the process flow in two or more branches. The Designer offers you two gateways to choose from (see Available Gateways below):

• Using the exclusive gateway is always tied to conditions. During modeling, you define one branch as default and add conditions to the other branches.

• Conditions can only have two results: Either the defined condition is fulfilled (true) or it is not fulfilled (false).

• Use the parallel gateway to enable independent, simultaneous processing of multiple process branches.

• The parallel process flows must be merged together with a second parallel gateway element.

Available gateway elements are:

BPMN Element	Usage	Details
	Splits the process flow in two or more branches, only one of the branches will be followed (based on the specified conditions). The conditions are provided in the execution model of the process flow(s) leaving the gateway element. Tasks and end events can have multiple incoming flows. You can use one of the task elements or the end event to merge the process flow split by an exclusive gateway.	See Exclusive Gateway
	Splits the process flow in two or more branches that will be executed in parallel. The order of execution of the parallel branches and the contained tasks is undefined and may vary between process instances. The parallel process flows must be reunited with a second parallel gateway.	See Parallel Gateway

Exclusive Gateway

When using the exclusive gateway, you can define one branch as default. You can do this with option Sequence Flow in the Attributes of the outgoing relations. The default flow is the branch that will be followed if none of the conditions apply:

The execution model Decision is created by default for all outgoing process flows of exclusive gateways. Use it to implement conditions on all other branches:

• If you use an exclusive gateway, only one sequence flow is selected.

• If no condition evaluates to true and you have not defined a default flow, the xUML Runtime will throw an exception. We recommend avoiding this scenario.

Please note that you cannot create an execution model on the gateway itself:

Parallel Gateway

When using the parallel gateway, you split the process flow into branches that will run independently from each other:

The only requirement for parallel process execution is already predefined: All process branches within the starting and the ending parallel gateways have to be fully executed bevor the process in the main branch may continue:

No further implementation is required, so it is not possible create an execution model on the gateway itself or on its flows: