10 BPMN Elements you Should Learn Before Creating a Business Process Diagram
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.
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.
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.
When 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.
Note 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.
Similar 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.
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.
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.
As 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.
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).
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.
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).
- 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].