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BPMN Style, an Introduction to Basic Principlesby Gregor Jošt and Gregor Polancic

While “style rules” are not part of the official BPMN specification, they greatly increase the clearness and readability of the models. In this paper, an introduction to basic principles of “style rules” is given, along with the practical examples.

Abstract

Considering that Business Process Model and Notation (hereinafter referred to as BPMN) is available since 2004 and has gained a worldwide recognition as de-facto standard of business process modeling, modeling practice is still in its infant stages. While many basic and common mistakes can make models difficult to understand, they can be avoided by carefully following the rules of BPMN specification. However, the notation itself does not provide a mechanism that would reveal the process logic in an unambiguous way.

As already discussed in previous paper, available on the official Good e-Learning’s website, several concepts, such as good practices, diagram patterns and basic methodology address such issues. These concepts are also referred to as the “style rules” of BPMN modeling. They are not part of the official BPMN 2.0 specification, but they greatly improve on clearness and completeness of BPMN models and provide consistency across the businesses [1].

Categories of Style Rules

Since the style rules of BPMN modeling consist of many different concepts, we can classify them into five basic categories, namely:

1) Architecture 2) Layout 3) Naming 4) Process Structure 5) Consistent Usage of BPMN Standard

Each of these categories has a set of specific style rules that correspond with the category type. In the following subchapters we will briefly introduce each of the aforementioned categories and provide a practical example.

Architecture

As a part of architecture, style rules address the very early stages of process modeling. Firstly, it is important to have a unified understanding of the process scope, namely identifying the key aspects of the process, such as who is part of the collaboration, what their activities are and so forth. Furthermore, it is important to identify different instances of our process. This allows us to get a comprehensive view of the process, which is a starting point for business process modelling. To this end, architectural aspect of style rules encourage unique names of our diagrams, which reflect the semantical content of the process. First and foremost, the diagram names should be unique. They may include numbers as well, especially when including sub-processes, which increases the understanding of the diagrams’ architecture. A simple example can be seen in Figure 1.

BPMN Series #13 | ATL001:13

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Numbering of the diagrams, such as displayed in the image above, comes to the fore when we operate with a large number of diagrams, since it provides a greater consistency among the models.

Layout

The layout aspect of style rules addresses the visual component of the models, namely the positioning of elements, their size and how they overlap each other. To increase the readability of the models, it is strongly advised to fit a BPMN model on one page, which can usually be achieved by incorporating Sub-processes. To this end, we begin with a top level diagram that represents the complete process and Sub-processes, to expand any additional detail. Also, such an approach reduces the number of possible errors.

Furthermore, layout style rules forbid any overlapping of edges and nodes. This greatly decreases the readability and understandability of models, which is represented in a simple example in Figure 2.

As can be seen from the figure above, the message flow is overlapping the “Receive order” activity. Also, both sequence flows that follow Event Based Gateway are overlapping, which reduces the readability and clearness of the model. By following the style rules, we can conduct a clearer model, as evident from Figure 3.

Naming

A BPMN model is in its essence a very powerful communication tool. To this end we want to provide the most effective way of communication and this is where the naming style rules become prominent.

Naming (or sometimes referred to as labeling) is therefore one of the main aspects of style rules. While there are no official naming conventions in the specification, a wide variety of best practices and recommendations have been conducted over the years.

Besides some basics tips, such as avoiding abbreviations, consistency between models and consistency in naming (namely, all elements that support labeling should be named), style rules address each of the five main groups of BPMN elements [2]: Swimlanes, Flow Objects, Connecting Objects, Data and Artifacts. Each element that belongs to a certain group has its own rules for naming.

For example, naming of Activities is essential, since it represents something that a participant in the process is doing. Since they represent work and not functions, naming of activities should be done in a verb-noun way, i.e. “Order pizza”. Any other naming, such as “Pizza ordered” or “Pizza ordering” is incorrect and not in line with style rules of naming.

Additionally, two Activities in a process model should not have the same name. However, if they represent the exactly same Activity, duplicating names should still be avoided in favor of Call Activities, as shown in Figure 4.

Figure 1: Architecture Style Rule

Figure 2: Node and Edge Overlapping

Figure 3: Absence of Node and Edge Intersection

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Process Structure

Process structure style rules address first and foremost the hierarchy of models, which is mainly achieved with the use of Sub-processes and Call Activities [3]. Each process level in such a hierarchy should fit a single page, to increase the readability of the processes. In case of complex models, further nesting is required.

Besides the hierarchy, process structure focuses on BPMN elements as well. A great deal of importance is given on Gateways, since they are the most common source for logical errors and ambiguity in process structure. To this end, the majority of style rules address the best practices in the field of splitting and joining of the flows with the use of Gateways. For example, the model in Figure 5 is in accordance with the BPMN standard, but it does not follow the style rules on two points.

Firstly, the multi merge in “Bake Pizza” Activity leads to a multiple execution of the Activity, which is incorrect in our case. Secondly, it is recommended that an Activity has only one outgoing sequence flow, to ensure the readability of the model. This is also violated in the “Bake Pizza” Activity, since it has two outgoing sequence flow. Figure 6 represents the improved model by incorporating some of the style rules.

As seen from the model above, following the process structure style rules we create both semantically correct and unambiguous models, consequentially increasing the clearness of the model.

Consistent Usage of BPMN Standard

While this part of the style rules may seem straightforward, a surprising amount of modelers, especially beginners and students, are not modeling in accordance with the BPMN standard. This might be mostly due to the fact that there is not a single chapter in BPMN standard that would summarize all syntactical rules, but are rather scattered in different chapters throughout the whole specification [1]. In this light, style rules focus mainly on:

1) Connectivity between different BPMN elements 2) When to use start and even events, and 3) When to use lanes and so forth.

Basically, style rules summarize the BPMN standard in a more user friendly way, by focusing on the most common syntactical mistakes.

Figure 4: A Partial Model, Representing Name Duplications in Activities

Figure 5: Incorrect Process Structure in a Partial Model

Figure 6: Correct Process Structure in a Partial Model

© Copyright 2015 Good e-Learning. All rights reserved. No part of this publication may be reproduced, resold, stored in a retrieval system, or distributed in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of the copyright owner. Such requests for permission or any other comments relating to the material contained in this document may be submitted to: marketing@goodelearning.com. Good e-Learning is a trading name used by

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Conclusion

In this paper we introduced the basic principle of style rules, which are classified into five basic categories, namely architecture, layout, naming, process structure and consistent usage of BPMN standard. We briefly described each category and provided a practical example for the most common representatives of each category.

While style rules are not part of the official BPMN standard, they greatly increase the clearness and readability of BPMN models. BPMN models are considered the most important communication tool in business environment, so every improvement to the model matters.

Want to learn more about specific category of style rules? Head over to the Good e-Learning’s website! 

References

[1] B. Silver, BPMN Method and Style, 2nd Edition, with BPMN Implementer’s Guide: A structured approach for business process modeling and implementation using BPMN 2.0. 2011, p. 286.

[2] Object Management Group, “BPMN Specification - Business Process Model and Notation,” 2015. [Online]. Available: http://www.bpmn.org/. [Accessed: 14-Jan-2015].

[3] Business Process Incubator, “Background on BPMN Modeling.” [Online]. Available: http://www.bpmnwebmodeler.com/background.html. [Accessed: 23-Jan-2015].