What are multi-instance activities in BPMN and how are they used?

Multi-Instance Activities or Tasks in BPMN are one of several forms of looping activities.  While looping can always be modeled in BPMN using a decision gateway and sending the flow backwards to an earlier point in the process, a multi-instance activity is a nice shorthand notation that can be used in certain situations.

BPMN Multi-Instance Activity

Multi-instance activities are denoted by three parallel lines at the bottom-center of the activity/task symbol.   It’s purpose is to show that the activity occurs for a collection of objects or items.  The number of times that the activity completes is defined by the number of items that exist in the collection.  Since the collection is delivered to the activity at the start, the number of repetitions is immediately know.  This is different than other looping mechanisms that must check a condition every time the loop completes in order to determine if it should continue looping.

Three vertical lines indicate that the multi-instance activity is non-sequential.  This means that the activity can be completed for each item in the collection in no particular order. 

Three horizontal lines indicate that the multi-instance activity is sequential.  This means that the activity must complete for each item in the order that they are received within the collection.

posted @ Friday, April 5, 2013 6:22 PM by Chris Adams