You can express an OR gate, otherwise known as an inclusive decision or merge, by drawing the gateway symbol and specifying the OR stereotype.
The OR gateway is drawn as a diamond symbol with a large circle in its center.
An inclusive OR decision is one in which one or more of the outgoing Sequence Flows from the decision can be taken. A useful expression that you can use to remember the logic of an Inclusive Decision (OR) decision is “one or the other, or both”. Again, there can be more than two output Sequence Flows.
BPMN specifies that there cannot be zero output flows: you must specify a flow as a default flow.
An inclusive OR merge is simply an OR gate, used to merge multiple Sequence Flows into one outgoing Sequence Flow. The logic of the inclusive OR merge is that the process flow continues when the first signal (a Token) arrives from any of the set of input Sequence Flows. If other signals subsequently arrive from the other input Sequence Flows, they are not used to continue the flow of the process.
To model an inclusive OR decision
1 Draw a Gateway symbol, and specify a stereotype of OR.
2 Draw Sequence Flow lines from the Gateway symbol to their respective process symbols. Open the definition of each Sequence Flow line, and in the Symbol tab, specify a condition for the flow line to be taken. For an inclusive OR, you must specify a condition for each outgoing Sequence Flow.
3 Specify a Default Sequence Flow:
Open the definition dialog box of the Sequence Flow line you have determined to be the default flow.
Click the Symbol tab, and then set Default to True.
This indicates that if the conditions on all alternative flows evaluate as False, then the Default path is taken. According to BPMN, it is not mandatory to specify a default outgoing Sequence Flow.
Note If you do not specify a default outgoing Sequence Flow, you must ensure that the condition on at least one of the other Sequence Flows evaluates as true. If not, the model is invalid.
The following image shows an example of an inclusive OR decision used in a diagram.
To model an inclusive OR merge
1 Draw a gateway and select the OR stereotype.
2 Draw two or more applicable Sequence Flows from their respective process to the gateway.
3 Draw an output Sequence Flow, from the gateway to its applicable process.
You must leave the Condition property of the outgoing Sequence Flow blank.
The following image shows an example of a Inclusive OR Merge used in a diagram.
