About Business Decision Modeling and DMN. Nowadays Business Decision Modeling is rapidly becoming major technological and methodological framework to support decision making approaches across a wide range of business problems from loan origination and insurance underwriting to clinical guidelines and recommendations. The recently introduced OMG standard “Decision Model and Notation (DMN)”  brings standardization to decision modeling, an emerging best practice. Decision Modeling clearly defines a business target, shows how to orchestrate decision management techniques, supports interoperability, and integrates decision models into modern enterprise architectures. DMN quickly becomes a mainstream approach supported by many Business Rules and Decision Management tools .
To Whom This Guide Is Oriented. This guide is oriented to people who want to build operational decision models for their own business environments. They’ve probably already looked at the DMN standard itself and quickly figured out that the text of the standard is more oriented to DMN vendors (implementers) than to practitioners. They’ve probably read or at least navigated through recently published DMN textbooks like -, which are trying to cover all (!) DMN aspects and to provide methodological recommendations for how to apply DMN in the real-world decision modeling.
Thus, we expect that our readers are already convinced of the value of the decision modeling proposition. However, they still have problems with understanding what actually should be done to build their own operational decision models.
How Readers Create Executable Decision Models. The objective of this guide is to help readers quickly learn how to apply the DMN approach to build working decision models. To achieve this objective, this book will guide readers on how to create working decision models for simple and complex business problems. More importantly, readers should be able to execute (!) their decision models and integrate them into their own IT systems. That’s why we called this guide “DMN in Action”!
While DMN is supposed to take care of future interoperability (tool independence), a reader needs to choose concrete DMN tools to actually create and execute decision models. Without using such tools it’s simply impossible to achieve our objective. So, as readers go through this guide, they can utilize the following tools:
- Microsoft Excel: without doubt the most popular tool among business analysts in any industry. Our readers will mainly use Excel as the best table editor to create and enhance business decision models.
- OpenRules: a highly popular open source business rules and decision management system. Our readers will use OpenRules to test (that assumes an ability to execute!) their decision models.
The website www.DmnInAction.com offers a reader two options: 1) open, analyze, and execute all decision models online without any download; 2) install a free evaluation version of OpenRules and analyze/modify/execute all provided or your own decision models.
Instead of Excel a reader may use Google Docs or Open Office. If a reader prefers to use a DMN implementation  different from OpenRules, they still can do it, but the described DMN constructs need to be adjusted to the tool-specific DMN representations.
How this Guide Is Written. This guide was written in style of dialog between the AUTHOR and the READER. The guide consists of multiple dialog-sessions, during which AUTHOR and READER are trying to build concrete decision models. They are freely discussing why and how they are actually building decision models, without avoiding any of the missteps, pitfalls, and alternative approaches.
From one decision model to another the AUTHOR will lead the inquisitive and receptive READER to different decision modeling concepts and notions emphasizing and/or demystifying especially complicated aspects, and attracting the reader’s attention to special situations that occur in the real-world decision modeling.
About the Reader. We consider the READER to be a subject matter expert or a business analyst without any programming experience. He or she may be proficient in Excel but more importantly is a person who really wants to understand how to build good decision models that can be adjusted and enhanced over time as business conditions change.
Only once, in the Dialog-Session 3, will the READER be joined by the DEVELOPER, who also will be “inquisitive and receptive” but from a purely IT integration perspective.
The actual reader of this guide will find this text to be perhaps more like a freely told story or, rather a freely conducted discussion. Being represented by a fictional READER, the actual reader will hopefully find the answers to a lot of his/her own questions, and will eventually gain an intrinsic understanding of the DMN-based decision modeling technique.
About the Author. The fictional AUTHOR in this guide represents me, Jacob Feldman, the Chief Technology Officer of the OpenRules, Inc., a US corporation that created and maintains the open source Business Rules and Decision Management system commonly known simply as “OpenRules” . Over the course of dialog-sessions I will try to share my multi-year experience as a decision modeling practitioner who has helped our customers develop and maintain production-quality decision models in various business domains.
I want to warn the readers that this guide by no means is a DMN textbook as it does not cover all the items introduced in the DMN standard. On the contrary, it concentrates on the most frequently used decision modeling constructs described in DMN and uses their particular implementations in the OpenRules formats.
As the AUTHOR, I took a liberty of choosing the DMN concepts that are most frequently used and helpful and those which should be avoided. I simply don’t mention some concepts currently included in the DMN standard which I do not recommend for use. In particular, the AUTHOR will not talk about hit policies with priorities or about pure programming constructs such as loops or if-then-else statements included in the DMN Friendly Enough Expression Language (FEEL). As the AUTHOR, I promised the READER to stay away from programming, and I will try to stick to this promise over the course of all (well, almost all) dialog-sessions. At the same time, the READER and I will actively use the FEEL syntax to represent various business expressions and calculation formulas.
The nice thing about the DMN standard is that it allows vendors to compete on different representations of the same DMN concepts as long as they have the same semantic meaning. The reader may find that OpenRules graphical representations of some DMN concepts are slightly different from examples included in the current DMN specification. For instance, we do not use single-character and double-character abbreviations for hit policies which are supposed to be placed into a separate cell of every decision table. Instead, we use keywords such as “DecisionTableSingleHit” or “DecisionTableMultiHit” in decision table titles.
Finally, I believe it is extremely important to keep this guide as small as possible (no more than 150 pages) and to allow the reader to start developing their own decision models ASAP. They can do this right after going through the first 3-4 dialog-sessions and actually modifying and executing the provided examples of decision models. In general, the guide provides many examples that can be used as working prototypes. Learning by example is the quickest and easiest way to learn fundamental decision modeling concepts.
How to Use this Guide. It is not necessary to read the entire guide. Even if you read only the first two dialog-sessions, you will get a good introduction to practical decision modeling techniques. The third dialog-session “Integration with IT” allows you to invoke your IT colleagues to make sure that your future real decision models will be as easily integrated into your specific IT infrastructure as it is explained in the guide using a simple example.
Each dialog-session starts with a list of the discussed topics, and you may skip sessions that are of no interest to you. So, you can read dialog-sessions in the presented order, or you may read them in accordance with your actual interest and needs.
What is really important is not just to go through the printed examples but also download, analyze, and execute the described decision models using the supporting software. It will allow you to look at all implementation details directly in Excel including the use of dropdown lists, data validation, cell merging, outlines, and other well-known and very helpful Excel constructs. All figures may also be seen directly in Excel by downloading the related projects from www.DmnInAction.com.
Supporting Software. This guide comes with the software that includes all described decision models in Excel format. To do this, visit www.DmnInAction.com website and you will be able to download them from the page “Decision Models”. You also may open OpenRules Why-Analyzer to select, analyze, and test all these decision models online without any downloads or installations.
If you want to download these decision models to your own computer and modify and execute them locally, you may receive the supporting software for free by submitting a request to OpenRules. Alternatively, you may get an evaluation copy directly from www.OpenRules.com and use it to run the existing or to create your own decision models.
I recommend you to check www.DmnInAction.com from time to time as it is being constantly updated with new decision models not described in this guide (yet).
Acknowledgments. First of all, I want to thank the subject experts with whom I was fortunate enough to work developing complex business rules, optimization and machine learning applications over the last two decades. Secondly, I want to thank all the people who helped to bring the DMN standard to the everyday reality for many decision management practitioners worldwide. It would not have happened without previous work and the current support by key architects and actual developers of various business rules and decision management products. Special thanks should go to the authors of the “big” books that together provide methodological guidance for business decision modeling techniques in general and the DMN standard in particular.
And finally, I want to share a little story about people who had no direct acquaintance with modern decision modeling techniques but who essentially incentivized me to write this guide. Many years ago, preparing for my university entrance exams, I read a math book simply known at that time among Soviet high school students as “Tarasov and Tarasova” (by the last name of the authors). The book was written in a very unusual style of dialogs between TEACHER and STUDENT. It was a really enlightening guide that not only demystified complex mathematical concepts but gave me an initial feeling of the beauty and intrinsic integrity of mathematics in general. Thank you, Tarasov & Tarasova!
Jacob Feldman, PhD
Monroe, New Jersey