18 September 2013

Notations for Business Process (Part 1) - RAD, EPC and BPMN

In several discussions I have had about process modelling methods, the methods being discussed are the types of notation or graphical notation used to represent business processes. The notations are always a topic of contention among business process modellers and practitioners. This is the first article of a series attempting to show with simple examples some of the commonly used business process modelling notations.


There are many graphical modelling notations or types of diagram that can be used to depict business process. Categorically they can be grouped into two major types based on the purpose of the diagram - (i) process context notations where the main purpose of the diagram is to define the context or landscape of business processes in an organisation; and (ii) process flow notations where the main purpose is to show flows of activities in business processes or across processes. Having said that a notation may be used intuitively across both areas.

In this article, we look at three types of process flow diagrams - Role Activity Diagram (RAD), Business Process Model & Notation (BPMN) process diagram and Event-driven Process Chain (EPC) diagram.

Role based versus Process centric

Role Activity Diagram (RAD)

Role Activity Diagram (RAD) is a notation originally developed in the UK, for process modelling in software development projects. As described in its name, RAD is a basic role-oriented process model, i.e. focusing on the jobs of specific roles and their interactions with others.

The key elements of RAD are:
  • roles,
  • actions or activities,
  • states,
  • choices,
  • creations and
  • interactions.
Figure 1: Example of RAD diagram

One of the key differences between a RAD and the other two process notations, EPC and BPMN, is that in RAD each role starts and ends with a state with actions happening in between the states of the roles. Actions change the state of a role and states start actions. Showing the states is not a requirement. Another key difference is with an interaction or hand over between roles which is explicitly shown in RAD inside all the roles associated with the interaction. In the example above, the action "give plan to designer" is drawn in both the project manager role and the designer role.

Event-driven Process Chain (EPC) Diagram

Event-driven Process Chain (EPC) is a part of the ARIS framework - a holistic modelling approach; ARIS stands for Architecture of Integrated Information Systems. The process chain (EPC) is the control view of the framework that is used to integrate the other views - organisation, data and functions views.

The key elements of EPC are:
  • events,
  • functions,
  • connectors, and
  • control flows.
Events trigger functions which represent units of work that take input and transform it to output. Inputs and outputs can be information or physical products.

Figure 2: Example of EPC diagram without lanes Figure 3: Example of EPC diagram with lanes

In EPC diagram, a process flow always start and end with events. While in RAD the states represent states of roles, here the events refer to stages of the process. When using lanes, the EPC diagram may look similar to RAD but noted the different approach in depicting hand-off between roles. Hand-off is shown simply with the control flow arrow. Events are place to denote an outcome of previous function and/or a trigger for the next function.

BPMN Process Diagram

BPMN stands for Business Process Model & Notation which is process modelling notation standard released by Object Management Group. BPMN process diagram is one of the three types of diagrams defined under the standard.

The key elements of BPMN process diagram are:
  • events,
  • activities (tasks or sub processes),
  • gateways, and
  • sequence flows.

Figure 4: Example of BPMN process diagram Figure 5: Example of BPMN process diagram with pool, lanes and intermediate events
Similar to the EPC diagram, a BPMN process flow always start and end with events. Intermediate events may be used as in Figure 5. Again like EPC diagram, in BPMN process diagram hand-off is implicitly shown with the sequence flow arrow.

This is a good time to concur on the key difference between role-based approach of RAD and process-based approach of EPC diagram and BPMN process diagram. While the hand-offs between roles are delineated in RAD, they are shown as flows between roles in EPC and BPMN, i.e. the flows are the orchestration of controls between roles.

Extending the Notations

Both EPC and BPMN process diagram have been enhanced or allow enhancement to the elements. The next two sections take a quick look at eEPC and BPMN with extension artefacts. the purpose of these extension is to enable graphical representation of additional information on a process diagram.

Extended EPC (eEPC) Diagram

Additional views are represented by enhancing event-driven process chains with notational elements providing richer information on process diagram.

Figure 6: Example of extended EPC diagram

The example in figure 6 only use a single function the earlier EPC diagram to illustrate some of the extended elements, including business unit, sales order file (input), inventory database (input), XYZ system (software application), packing order (output) and identified weakness/risk. There are many other extended elements that ould be included depending on the objectives of your process modelling.

These extended elements in eEPC are standard extensions and can be found in most modelling tools supporting EPC and eEPC. These extended elements are also used across other areas of the ARIS framework.

Extended BPMN Process Diagram

The BPMN 2.0 specification enable additional notational elements through the use of extension artefacts which can be applied to offer additional views and richer information.

Figure 7: Example of BPMN diagram with extension artefacts

Figure 7 is an illustration of a BPMN process diagram using extension artefacts representing similar information displayed in figure 6. The elements on the right are part of the BPMN 2.0 elements. The four symbols on the left are extension artefacts I have added in my modelling tool for illustrating usage of BPMN extension artefacts.

Although artefact extension is a feature in BPMN 2.0, the extended artefacts (elements) are non standard. This means that depending on the modelling tool that support artefact extension, varying artefacts could be introduced. The symbols implemented are restricted to within the organisation or even projects and require a common definition.See the article Using Extension Artefacts in BPMN Process Model for more information.
One crucial difference between EPC and BPMN elements is that the BPMN elements come with type attributes that enhanced its library of elements. Being a stand alone process notation, its elements and element types allow a BPMN process model to cover almost all potential scenarios. For instance, event elements has four major types - start, end, intermediate and boundary. Each of this could be further classifiedinto several sub types such as message, timer, escalation, conditional and so forth. All these process centric characteristic is not possible to be represented in an EPC diagram.


To sum up the key differences again, EPC and BPMN process diagrams are process centric where as RAD is role-based. Although both EPC and BPMN process diagram can depict roles, its nature of being process centric require the modeller working on it to have the view of a business process and not just roles and activities. The extension feature in EPC and BPMN is very useful and provide powerful view if applied appropriately. Very likely at the different stages in your BPM practice and process modelling, different extended elements are applied.

In the next article, I will explore other notations for capturing business processes, particularly those commonly used in business process documentation projects.