10 BPMN elements you should learn before creating a business process diagram

BPMN, which stands for Business Process Model and Notation, is the ISO and de-facto standard for business process modeling.

Essentially, BPMN consists of a notation, which can be used to create visual diagrams, and an underlying meta-model, which enables IT systems to interpret business process models.

Since BPMN tries to address the representation of business processes at both a human and machine level, its notation is precise and comprehensive, consisting of over 100 different elements. Mastering the complete set of BPMN elements is quite a challenge, but fortunately you do not need to all BPMN elements at once. If you are just starting out with BPMN, you should focus your attention first on the top ten BPMN elements.

The top ten BPMN elements were ranked in a survey performed in 2008 by Muehlen and Recker, in which the authors analyzed frequencies of individual BPMN elements across 126 business process diagrams. They represent a sub-set of the descriptive class of BPMN 2.0 elements.

bpmn key elements1. (Abstract) Task

In general, a task is an atomic activity within a process flow. A task is used when the work in the process cannot be broken down to a finer level of detail. Generally, an end-user and/or applications are used to perform the task when it is executed. The most commonly used task in an abstract task (aka task), which has an undefined task type. In a BPMN diagram, a task is represented with a rounded rectangle. The next figure shows an example of three task types that can be found in an typical online store process.

bpmn key elementsSince a task represents an action, not a function or a state, a task should be labelled with a “verb-noun”, for example “Ship item”.

2. Sequence flow

A sequence flow is used to show the order that activities will be performed in a process. It is represented by a solid arrow. The next figure shows the three common online store tasks, but now connected by sequence flows.

bpmn key elementsWhen interpreting the meaning of a sequence flow, remember that when the node at the tail of a sequence flow completes (e.g. the item is selected), the node at the arrowhead is able to start (e.g. paying an item).

3. (None) Start event

As the name implies, a start event indicates where a particular process will start. A none start event does not have a defined trigger, i.e. it usually means that the corresponding process is manually started by a task performer. As shown below, a start event is always represented by a circle with a single thin border.

bpmn key elementsNote that a start event is optional – the BPMN 2.0 specification states that a process may have a start event. However if an end event has been defined, the process must have at least one start event.

4. (None) End event

An end event indicates where a process will end. In terms of sequence flow (see above), an end event ends the flow of the process, and thus, will not have any outgoing sequence flows. A none end event indicates that no signal is thrown when a process reaches its end state. As you can see below, an end event is represented as a circle with a single thick border.

bpmn key elementsSimilar to start events an end event is also optional, however, if a start event has been defined, the process must have at least one end event. Note that if several end events existed, a process is only completed when all process paths reach their corresponding end state.

5. Exclusive gateway

An exclusive gateway (aka XOR gateway) is used to create alternative paths within a process flow. As shown in the next figureit essentially creates  a “diversion point in the road” for a process, where only one of the paths can be taken. An exclusive gateway has a diamond shape with an “X” symbol draw inside. Alternatively, the “X” symbol can also be left out, where there is no difference in meaning between the two.

bpmn key elementsNote that a gateway does not perform a decision, it just tests a data condition (the decision is usually performed by an activity, prior to the gateway).

6. Parallel gateway

A parallel gateway (aka AND gateway) is used to synchronize (combine) parallel flows or to create parallel flows. It is distinguishable from the exclusive gateway by a “+” symbol inside the diamond. In the figure below you can see a parallel split and a parallel join.

bpmn key elementsAs you can see, without a parallel join the “ship item” activity would be performed twice – once when “prepare invoice for delivery” ends, and once when “prepare item for delivery” ends.

7. Pool

A pool is the graphical representation of a participant in a collaboration (a collaboration consists of at least two participants). A ‘participant’ can be a specific partner entity (such as a company) or can have a more general partner-role (such as a buyer, seller, or manufacturer).

A pool may include a process (aka white-box pool) or it may be empty (aka black-box pool). Below you can see an online store collaboration, consisting of a black-box and white-box pool.

bpmn key elementsAs evident from the above figure, a pool acts as a container for sequence flows between activities, where sequence flows cannot cross the boundaries of a pool. That is, a process is fully contained within the pool. The interaction between pools are shown through message flows, which is the next key BPMN element on the list.

8. Message flow

A message flow is used to show the flow of messages between two participants (i.e. pools) that are prepared to send and receive them. A message flow is represented by a dotted arrow (see below) and can connect to any type of activity, a black-box pool and a message event, which is presented next.

bpmn key elements9. Message start event

A message start event indicates that a message arrives from another participant and triggers the start of the process. A message start event is represented by a message symbol inside a circle with a single thin border (see figure below).

bpmn key elements10. Text annotation

Text annotations enable a process modeler to provide additional information for the reader of a BPMN Diagram. A text annotation can be connected to a specific element on a BPMN diagram with an ‘association’ (dotted line). This association will not affect the flow of the corresponding process.

bpmn key elementsConclusion

Here we have presented 10 key BPMN elements that are used in almost all BPMN process and collaboration diagrams. They represent a subset of the descriptive class of BPMN elements, and were initially identified in a research exercise performed by Muehlen and Recker (2008).

Sources used:

  • M. Z. Muehlen and J. Recker, “How Much Language Is Enough? Theoretical and Practical Use of the Business Process Modeling Notation,” in Proceedings of the 20th international conference on Advanced Information Systems Engineering, Berlin, Heidelberg, 2008, pp. 465–479.
  • B. Silver, BPMN method and style: a structured approach for business process modeling and implementation using BPMN 2.0. Aptos: Cody-Cassidy Press, 2011.
  • OMG, “Business Process Model and Notation version 2.0,” 03-Jan-2011. [Online]. Available: http://www.omg.org/spec/BPMN/2.0/. [Accessed: 15-Mar-2011].

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Gregor received his PhD in 2008 in the fields of software engineering and information systems and has nearly a decade of experience in BPMN, starting to investigate and actively use BPMN since its introduction in 2004. In addition, he has participated in the development of one of the first BPMN modeling utilities - a package of plugins for Visio, which were introduced early in 2005 and is the main author of the first BPMN poster (bpmn.itposter.net), which has been translated into several languages and already exceeded 50.000 downloads.