Gateways are modeling elements in BPMN, which are used to show converges and diverges of a Business Process. Usually, a diamond is described to represent a Gateway.
Overview of Gateways
Gateways play the following two roles.
- Join some processes together (Join of Sequence Flow)
- Split a process into some (Split of Sequence Flow)
A Gateway sometimes plays one of these two roles, and sometimes plays both at the same time. In a word, when a token arrives at a Gateway, Sequence Flow converges, diverges, or develops both convergence and divergence at the same time. However, a Gateway cannot be the target or a source for the message flow.
|Figure 1: Example of "Join"||Figure 2: Example of "Split"|
For a Gateway, a diamond drawn with a single thin black line must be used. It is not required that incoming and outgoing Sequence Flow should connect to the corners of the diamond. Sequence Flow can connect to any position on the boundary of a diamond. an internal indicator (marker) shows the type of Gateway (see below).
Type of Gateways
Based on the behavior of flows, the gateway is classified into four types. Each type of Gateways has two types of flowchart: Split/Decision, and Join. Split/Decision corresponds to divergence, while Join corresponds to convergence. The following explains the role of Decision Gateways for convenience's sake.
- Exclusive Gateways (XOR)
- Exclusive Gateways play a role to select one Sequence Flow from several Sequence Flows. In addition, it is classified into Data-Based and Event-Based.
- Depending on it that the conditional expression proposed by an outgoing Sequence Flow is true or false, one Sequence Flow is selected from several Sequence Flows. Among Gateways, this type is used the most.
- Depending on Events coming from the outside, one Sequence Flow is selected from several Sequence Flows.
- Inclusive Gateway (OR)
- Inclusive Gateways play a role to select some from several Sequence Flows, which suit the condition (the conditional expression is true). At least one Sequence Flow must be selected.
- Complex Gateway
- A Complex Gateway is used when the other three Gateway types are not appropriate for the process. In order to continue processing, at least one Sequence Flow must be selected.
- Parallel Gateway (AND)
- Parallel Gateways select actions of Sequence Flows all at once.
In BPMN, Gateways can define all actions of Sequence Flows of a Business Process. The table below displays the combination of the name and the used marker for Gateways.
|Types of Gateways||Types of Flowcharts||Marker|
|Data-Based Exclusive Gateways||XOR-Split,XOR-Join|
|Event -Based Exclusive Gateways||XOR-Split,XOR-Join|
- Business process diagram
- Sequence Flow
- Conditional Sequence Flow
- Default Sequence Flow
- KATO, Masato “An introduction to Business Process Modeling by BPMN”, Soft Research Center, 2006. (Japanese) ISBN:978-4-88373-226-5
- Associated with Business Process Modeling Notation (BPMN) 1.1 (2008).
- BPMN Introduction Episode 4: Can We Define Business Systems Only With BPMN Diagrams?(07/03/2009)