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

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

BPMN vs. EPC revisited, part 1

There were several posts and discussions on the topic of “BPMN vs. EPC”. One of them is quite comprehensive and its discussion thread very interesting. But there are still many important points untouched and I’d like to share some of them for those facing a choice of business process notation.

That doesn’t mean that there aren’t other options. But they have quite lower utilisation potential and/or address different needs. Certainly if UML is used, a combination of activity, statechart and sequence diagrams would do, more or less. And then most of what EPC offers could be expressed with ArchiMate. Speaking of process modelling notations it’s worth mentioning also Petri-Net which has better execution semantics than BPMN (while that’s the main claim of BPMN) but is not at all adopted by the business and generally gets little attention outside academia.

So, having the long and successful history of EPC usage and the current growing popularity of BPMN, it seems a valid set of options. And there is a demand for more information to support decisions related to the choice of process notation, especially (naturally) among ARIS users.

The ideas here are based on the conviction that a single notation for business processes which can equally serve the requirements for analysis, process automation and enterprise architecture is achievable. There are some strong points by the advocates of the concept that the choice of the notation should be based on the modelling objective and it’s fine to have many languages. However, if one notation is able to serve the majority of applications, then it would eventually be a better means for communication and will require less learning and maintenance.  Furthermore, when efforts for improvement are focused on one language, there is higher probability of getting it better sooner.

Having said that, I still hope that the information in this article would support not only XOR but also AND decisions. Another way to help such decisions would be to make a condition comparison, with a lot of “it depends”, if-clauses and suchlike. That is a valid approach but it will be avoided here leaving the “it depends” as conclusion for the readers, rather than using it as a way to structure the comparison. And speaking of structure, it would be quite loose – a dozen of short sections that could be read in any order.

One more thing before the actual comparison. I assume the readership of this article is familiar with BPMN and/or EPC. And, unless explicitly stated, by ‘BPMN’ I would refer here to its version 2.0 and ‘EPC’ would mean the extended Event-driven Process Chain. And when referring to EPCs I’ll use ‘gateway’ instead of ‘rule’ and ‘activity’ instead of function just for the sake of easier comparison. Hope you don’t mind.

Expressive power

BPMN features over a hundred modelling constructs. Most of them are sub-types of the three main flow elements. They are primarily focused on describing workflow and collaboration. As it can be expected, BPMN has much more expressive power than EPC in these two areas. The control flow elements of EPC are only five.

There are different ways (and viewpoints) to measure the expressive power of modelling languages. One of them is by workflow pattern analysis, another by ontology-based analysis and yet another by measuring the ability to integrate different aspects of Enterprise Architecture.

Workflow pattern analysis has been applied for comparison of BPMN 1.1 and EPC among other modelling languages by Nick Russell et al in 2006. According to this research, BPMN natively provides clear support for 24 of 43 patterns, while EPC supports only 10. Of course the real implications of that could be seen if there is a reliable statistic on the frequency of occurrence and the importance of unsupported patterns. Still, when you need to describe a workflow with more rigour and provide a model that is closer to reality, BPMN is the way to go. This is also confirmed by a more recent comparison between BPMN and EPC on the twenty main workflow control patterns.

Applying ontology-based analyses like the representational analysis of process modelling techniques, confirm expressive superiority of BPMN over EPC on the way it facilitates clear descriptions of real-world domains. (For those who don’t know and/or don’t care about this type of analysis, let’s just say that evaluation support of workflow control patters is not the only way to measure expressive power.)

However, if measured by the ability to integrate different aspects of Enterprise Architecture, EPC is much more expressive than BPMN. There will be some more information about this further in the post.

When evaluating the expressive power, it’s worth reminding that expressiveness comes with the price of increased apparent complexity. This reduces comprehension and communication effectiveness, especially among model readers that are not experts in process modelling.

Readability and efficiency

Which one is easier to read? And by whom?

That’s probably quite subjective. Some find BPMN event symbols more intuitive than the big hexagonal symbols for EPC events. Others defend EPC events for they somehow make you put a name unlike ‘none’ BPMN start and end events which are quite often left unnamed. Both are valid points and worth considering.

There is some research on the subject of process diagram readability but not much. This one applies cognitive effectiveness criteria based on the 5 principles introduced by Moody and Hillegersberg: representational clarity, perceptual discriminability, perceptual immediacy, visual expressiveness, and graphic parsimony. It seems EPC is doing a bit better there than BPMN.

When it comes to efficiency, BPMN diagrams are more compact than those of EPC expressing the same content. That’s not only because of the relatively smaller event symbols. EPCs require events after OR and XOR gateways, while in BPMN their semantics is conveyed by the attributes of the sequence flows following the splits. Moreover, the allowance of implicit events in BPMN as well as conditional sequence flows can make some diagrams really compact. Sometimes, however, this increased efficiency can lead to erroneous comprehension.

A smaller number of visual elements can indeed increase readability simply because there is smaller amount of things to comprehend.  In other cases more compact diagrams such as the ones using implicit events and/or conditional sequence flows are not necessarily easier to read. They can take more time to understand and are prone to misinterpretation.

Resources assigned to activity

Quite often one single activity involves more than one participant at the same time. EPC not just supports this but offers more than ten different connection types between participant (organisation unit) and activity (function).

In BPMN on the other hand, assignment of multiple resource to one activity is natively not supported at all. There are some attempts to do it like those proposed by Michele Chinosi in one of the chapters of BPMN 2 Handbook. I’m not convinced by those workarounds.

Generally EPC is superior to BPMN when it comes to resource analysis, not just of human resources, but also in integrating data and system objects that can be further detailed in other Enterprise Architecture views. More on that in the next section.

One good solution offered in ARIS to solve this is to assign Function Allocation Diagrams (FAD) to BPMN activities. FADs can contain objects like organisational units, application systems, services, risks, data and more than one hundred other objects. But that’s a specific extension and it’s more or less barrowed from EPCs as FADs are introduced to reduce the complexity of rich process chains.

Enterprise architecture

EPC is a process-centric Enterprise Architecture method in itself. I personally don’t see the point of separating BPM and EA. And at the time there was only EPC (sorry, I don’t count flow-charts and suchlike as a way to describe processes), there wasn’t any separation between BPM and EA. And it’s strange when aiming IT/business coherence how first EA was separated from BPM and then how BPM became BPA to allow for business process execution to get the BPM label. Anyway, let’s not go into this here. The talk is about business process notations. Those who believe there should be a rigorous way to integrate process control flow with data, systems, products, services and infrastructure, will have that natively supported by EPC.

BPMN is not made for that. But we can’t say it as an objective not achieved. There wasn’t such objective in the first place. One way to partially support some EA aspects is by adding artifacts (but unfortunately not different types of associations). Another is to integrate with some EA notation such as ArchiMate. What would still be missing is the support of the motivational domain. And that’s another advantage of EPCs. There you can link activities to requirements, objectives and KPIs.

 

Well, that (+comments, hopefully) should be enough for Part 1. Next one will deal with handling of end-to-end processes, exceptions, sub-processes, messages, unstructured processes, loop, data and more.

 

Special thanks to Roland Woldt who reviewed the draft of this post and provided some valuable advice.