Describe the BPMN Complex Gateway and how it is used in process modeling?

BPMN Complex Gateways can be used for splitting or merging a complicated process flow scenario.  Complex Gateways are not often used in BPMN since the simpler and more well understood parallel, inclusive, and exclusive gateways handle most situations.  For a refresher of how each of these gateways work you can review the following:

BPMN Parallel Gateway
BPMN Inclusive Gateway
BPMN Exclusive Gateway

However, for more involved scenarios that use complex sequence flow rules the BPMN Complex Gateway can actually simplify your model by eliminating complicated combinations of multiple gateways. 

A Complex Gateway allows the modeler to specify any arbitrary rules needed to determine how to emit tokens or process arriving tokens.  The example below shows how the BPMN Complex Gateway could be used for an interview process where references have been requested for a particular candidate.  The process is intended to request 5 references, but for the sake of time it will proceed after receiving only 3.

BPMN Complex Gateway Example

This example diagram shows the process with a placeholder (dotted diamond) for a gateway. 

If no gateway is used then the flow is never synchronized and the tokens will continue on to the next task as each token is received.  This is not how we want the process to work.  An exclusive gateway would behave the same way when used to merge flows.  If a parallel gateway is used then the gateway would wait for all 5 tokens to arrive before proceeding.  This also is not how we intend for the process to work.  Similarly, an inclusive gateway waits for all tokens that were emitted from the corresponding splitting gateway.  Therefore, in this instance the best solution is the Complex Gateway.  

BPMN Complex Gateway Example

The complex gateway is coupled with an annotation where the specific rules for processing the tokens are described.  We can clearly state that the process will proceed once 3 (of the possible 5) references are received.

Bigazi provides a nice YouTube simulation of the Complex Gateway 

posted @ Saturday, July 6, 2013 4:56 PM by Chris Adams