BPMN vs. EPC revisited, part 2

The previous part focused on areas such as expressive power, readability and enterprise architecture. This one, written jointly with Roland Woldt, dwells on a few more aspects such as semi-structured processes, exceptions, loops and data handling. Some of them could be sorted well under the ‘expressive power’ heading but as stated in the previous post, the intention is just to put some structure to the ideas and experience shared, not to give a list of criteria. If in spite of that the sections are regarded as comparison criteria, then each should get some weighting based on the application objectives. Additionally the ‘points’ should be reduced by the ‘cost’ of the advantage. For example, more expressive power brings increased complexity.

But again, as this was not the intention, the content is not suitable for such usage.

Semi-structured processes

A business process model is meant to show some structure and behaviour patterns that are known or at least expected with a good degree of certainty. For processes with high uncertainty, using a notation – no matter how good – would not be as useful as for well structured processes.

There are processes for which activities are known but not their sequence or number of performances. These types of processes are supported by BPMN via ad-hoc sub-process. No similar construct is offered by EPCs.

Advantage: BPMN

Business process notations are used in some way even for managing unpredictable processes. Interestingly, Adaptive Case Management systems such ISIS Papyrus, support both EPC and BPMN which is yet another example that each one has strengths in different application areas.

Exceptions, transactions and compensations

Both EPC and BPMN can support exceptions. However, there is no way to show that something happens during the activity execution in an EPC. Conversely, BPMN is rich in constructs that support exceptions. Those include the boundary events in combination with catch/throw semantics. Situations where an exception could happen everywhere within a process fragment are also well supported by putting the fragment in a sub-process with an exception boundary event. Additional benefits are provided by event sub-processes.

Exception handling is really important. Some claim that this is so only from IT perspective, but I doubt that. However, it is true that some modelling limitations tend to support wishful thinking and many processes are suffering of the ‘happy path syndrome‘. Now, the mere existence of so many exception handling constructs in BPMN might – well, at first frighten but then – prompt some more realistic business representations.

If we are completely fair with EPC, we should admit that there some activity interruption is supported. But this will mean to depart the pure notation discourse. There is an attribute ‘interruptible’ which, when set to “true”, will allow activity execution to be interrupted based on specific resource assignment. This capability is supported by ARIS Business Simulator. A token arriving at an activity will trigger it but when this activity is interrupted (attribute ‘interruptible’=true), it will wait until the activity performance is resumed. The reason for such interruption could be that the resource carrying out the activity has stopped working because of a break.

However, in addition to “interrupting” events BPMN supports “non-interrupting” events that trigger an exception while the process continues – you can show this in EPC with rules (“and” rule) and events, but the solution in BPMN is more elegant.

Transactions and compensations are supported by BPMN and not at all by EPC.

Advantage: BPMN.


Loops -either standard, parallel or sequential- are a powerful construct in the BPMN notation. They allow to show that a process can run multiple times without the need to draw confusing lines in a model or to repeat process fragments over and over again. In combination with using events or attributes that hold the number of repetitions this is a clean and easily understandable way to model.

Loops can also be shown in EPC notation, even though there are no special markers in the functions that shall be repeated. A modeller has to work with multiple events that are coordinated by rule objects (e.g. “and”) to describe the conditions when a loop or repeating activity has ended. This is not impossible but a less elegant solution when the process becomes more complex.

Additionally, BPMN provides 11 standard attributes for handling loop behaviour. When such formalization is needed, things like loop cardinality, data-based conditions and how multi-instances a produced by the activity can be specified.

Advantage: BPMN

Managing data

BPMN assumes that all data is freely available within a process and can be used in the tasks whenever needed. In addition to this data highlights can be shown by either using the data object or the data store for persistent data (even though persistence means “only for this process instance”). The notation is not meant to allow data modelling and the breakdown of data information in specific data models > see chapter 7 of the specification.

In opposite to this the EPC notation allows multiple ways to show data in a process: either as abstract clusters or technical terms, that describe an information, or depicted as information carriers, such as documents, CDs, etc. And even as fine as showing relations to classes and attributes. The biggest advantage of using an abstract data object lies in the capability of the ARIS overall method -not only the EPC notation- to decompose a cluster into entities and then into its attributes. These can then be mapped to tables or even synchronized with other dedicated data modelling tools like ERWIN (via a 3rd party interface). Strangely, EPC allows better integration between process models and UML Class Diagrams than BPMN do, while both UML and BPMN are maintained by OMG.

Advantage: EPC

Process notation for ERP Systems

As mentioned earlier the EPC notation became very popular when the ERP wave took off and companies had the need to figure out and model their processes. The most popular example here is SAP and until today all SAP ARIS customers use this notation to synchronize three levels of process models directly with SAP’s Solution Manager. In addition to this, EPCs can be used to create test cases that get synchronized with HP’s Quality Center for testing (either through Solution Manager or directly via export from ARIS). There is no BPMN synchronization in place as of today.

To further accelerate the modelling efforts SAP provides two sources of process information that can be included into the blueprint models: The “Business Process Repository” (the transactions) and the “Enterprise Service Repository”. Both sources will be enhanced by non-SAP and manual steps in the blueprinting phase of the ERP implementation.
But SAP is not the only ERP system on the market – its largest competitor Oracle OEM’ed ARIS in its “BPA Suite” tool and in that, the EPC notation is also the standard notation. Opposite to the SAP synchronization, the EPCs will be transformed into BPEL models that then will be exported as BPEL and WSDL files that can – after running an Oracle-specific script that transforms the standard BPEL export file into an Oracle-specific format – then be imported into the Oracle ERP system.

Similar approaches to the BPEL export have been implemented in process modelling for Microsoft BizTalk and IBM’s WebSphere products.

An interesting way was presented by Software AG in the “Enterprise BPM” approach at CEBIT this year. Here it is also recommended to model the business processes in EPC notation, since it is easier to understand for business users and fits into an Enterprise Architecture without workarounds. After the business model is approved it can be transformed into a logical BPMN 2.0 model and then enhanced with technical information, for example to show a split of a business process step like “check inventory” in multiple service steps. After the logical BPMN model is ready it can be pushed into webMethods where the physical BPMN model then gets implemented.

The last use case shows an implementation of the original purpose of the BPMN notation. I expect similar approaches for creating a true business process architecture, while being able to execute the lower level models from other vendors too.

Advantage: EPC

Tools support

An interesting observation nowadays is the marketing hype around BPMN. To a new user, who is investigating which notation/which tool should be implemented the options and sometimes conflicting marketing information are confusing. On the one side you hear that EPC is a proprietary notation (which is not true) that is only supported by ARIS, on the other side, the EPC templates ship with a standard MS Visio installation for years now, while BPMN (in the old version 1.2) was just introduced to the latest version Visio 2010. In addition to this a quick Google search will show dozens of tools for either notation.

I think the best approach to choose the right tool is to ask yourself about the goals of a BPM/EA implementation. Do you “just” want to model simple processes, shall they be executed in a BPMS or used in an ERP implementation, or is the procurement of a tool just the start of a larger, enterprise-wide implementation with the goal of creating and measuring a performance-driven organization, while using enhanced capabilities such as simulation, process costing or process performance management. Both cases depend heavily on the maturity of the organization and luckily the established vendors provide import capabilities for existing information.


By Ivo Velitchkov and Roland Woldt