BPMN diagrams

Definition

BPMN (or "Business Process Modeling Notation") diagrams support business process modeling.

A BPMN diagram is constructed around activity flows ("Tasks" and "SubProcesses"), associated with flow control events ("Events" and "Gateways"). Other elements central to a BPMN diagram are structuring elements oriented around process participants ("Pools" and "Lanes"), and artifacts produced and consumed by activities ("DataObjects").

The main aim of BPMN is to provide notation that is truly understandable by all company users including:

· business analysts who create the preliminary outline of procedures

· developers who are in charge of implementing the technology that will run procedures

· company users who will manage and apply procedures.

In this way, BPMN provides standardized notation to bridge the gap between business process modeling and process implementation.

An example of a BPMN diagram is shown in the figure below.

An example of a BPMN diagram

BPMN elements

The following table provides an exhaustive list of all the elements that can feature in a BPMN diagram.

Element type	Icon			Element
Elements				Task
				MultipleInstanceTask
				ActivityLoopingTask
				SubProcess
				MultipleInstanceSubProcess
				ActivityLoopingSubProcess
				Transaction
				Group
				DataObject
				CompensationTask
				Pool
				Lane
				TextAnnotation
Gateways				ExclusiveGateway
				EventBasedGateway
				InclusiveGateway
				ComplexGateway
				ParallelGateway
Events	Start	Inter	End
				Event
				Message
	N/A			Error
	N/A			Cancel
	N/A			Compensation
			N/A	Timer
			N/A	Rule
				Link
				Multiple
	N/A	N/A		Terminate

Tasks

A "Task" is an atomic activity participating in a process. It represents a process activity that cannot be broken down into sub-activities.

Four activity sub-types exist:

· Tasks

· LoopTasks

· MultipleInstanceTasks

· CompensationTasks

Element	Role	Creation icon
Task	Atomic activity participating in a process.
LoopTask	Iterative atomic activity.
MultipleInstanceTask	Iterative atomic activity that can contain several parallel instances.
CompensationTask	Compensation activity triggered following the failure of a transaction.

CompensationTasks 

A CompensationTask is an activity triggerered by a CompensationEvent.

In BPMN, an activity can be considered as a transaction. If a transaction fails, the CompensationEvent is triggered and the CompensationTask run.

A CompensationTask cannot have outgoing flows.

Example of a CompensationTask

SubProcesses

A SubProcess is an activity participating in a process that can contain other activities and controls. SubProcesses are used when it is necessary to describe the behavior of an activity in more detail.

Three SubProcess sub-types exist:

· ActivityLoopingSubProcesses

· MultipleInstanceSubProcesses

· SubProcessReferences 

Element	Role	Creation icon
SubProcess	Subdivisible activity participating in a process.
LoopSubProcess	Iterative subdivisible activity.
MultipleInstance SubProcess	Iterative subdivisible activity that can contains several parallel instances.
Compensation SubProcess	Subdivisible compensation activity triggered following the failure of a transaction. A CompensationSubProcess cannot have outgoing flows.

Gateways

Gateways are activity flow control elements that manage flow divergence and convergence.

The notions of "Fork", "Join" and "Merge" are implemented through gateways, as are conditions.

Five types of gateway exist:

· ExclusiveGateways

· InclusiveGateways 

· ParallelGateways

· EventBasedGateways

· Complex Gateways

Element	Role	Creation icon
ExclusiveGateway	An ExclusiveGateway is used when the process flow divides into two or more flows. As the process proceeds, only one of these flows is taken (XOR).
InclusiveGateway	An Inclusive Gateway is used when the process flow divides into two or more flows. As the process proceeds, several outgoing flows can be simultaneously taken (OR).
ParallelGateway	A ParallelGateway is used to manage parallel flow creation and syncrhonization. As the process proceeds, all outgoing flows are simultaneously taken.
EventBasedGateway	An EventBasedGateway is used when the process flow divides into two or more flows. An EventBasedGateway's outgoing flows are "Flows" linked to "IntermediaryEvents".
ComplexGateway	A ComplexGateway is used when the process flow divides into two or more flows. A ComplexGateway is used in situations where other types of gateway cannot be used.

Forks

To define a Fork, a ParallelGateway is used, as shown below.

Using a ParallelGateway to define a Fork

Joins and Merges

To define a Join or a Merge, a ParallelGateway is also used.

Using a ParallelGateway to define a Merge

Events

The notion of event is used to represent "something that happens" during the execution of the process. These events affect the flow of the process.

Three types of event exist:

· StartEvents, which trigger the process.

· IntermediateEvents, which take place between the start and the end of the process.

Ø IntermediateEvents can intervene during the process flow, signifying that an event must be triggered in order for the process to continue (as shown below).

Ø An IntermediateEvent can intervene alongside a Task or a SubProcess. In this case, it represents an event triggered during the execution of the activity (as shown below).

· EndEvents, which mark the end of the process.

Element	Role	Start	Inter	End
Event	Any event.
Message	Event implying the reception or sending of a message.
Error	Event implying the triggering of an error.	N/A
Cancel	Event triggered when a transaction is cancelled.	N/A
Compensation	Event triggered when a transaction fails.	N/A
Timer	Event linked to a specific date or a temporal cycle.			N/A
Rule	Event triggered when a rule becomes true.			N/A
Link	Event used to connect the end of one process to the beginning of the next.
Multiple	Event resulting from the composition of other types of event.
Terminate	Event used to indicate that all activities on the process must be immediately suspended.	N/A	N/A

Swimlanes

Swimlanes represent a participant in a process. They are used as containers and organize the process around participants.

A swimlane can contain "Pools", high-level containers, and "Lanes", which represents sub-divisions of "Pools".

Element	Role	Creation icon
Pool	A Pool represents a participant in the process. Pools are used as high-level containers and organize the process around participants.
Lane	A subdivision of a Pool.

Artifacts

Element	Role	Creation icon
DataObject	Artifacts produced and consumed by the activities of the process.
Transaction	A "Transaction" is a diagram region used to represent the existence of a transaction containing all the activities present.
Group	A "Group" is a diagram region used to group together the process' elements.

Flows

Flows are used to link and sequence process elements.

Element	Role	Creation icon
Flow	Flow used to sequence two of a process' activities.
ConditionalFlow	A conditional flow.
DefaultFlow	A default flow.
MessageFlow	Flow used to make a message transit between two of a process' entities.

Activity sequencing

Example of activity sequencing

Using ConditionalFlows and DefaultFlows

A conditional branch can be expressed in two different ways using ConditionalFlows and DefaultFlows:

· Through the use of a Gateway, as shown below :

· By directly attaching Flows to Tasks (see figure below). This makes the presence of an InclusiveGateway  implicit.