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An Introduction to the “Decision Model and Notation” Standard

Posted by Rick Strempler on Feb 14, 2014 4:21:21 PM

The Object Management Group (OMG) is defining a new standard for decision modeling: Decision Model and Notation (DMN). If you aren't familiar with the OMG, they are an organization whose goal is to develop standards by reviewing and refining commonalities between existing models and notation.

On the downside, you might have already realized that you'll be introduced to a host of new three-letter acronyms. On the upside, this new standard addresses a gap that exists in defining and modeling decision logic. If you are a business analyst, you probably recall the first time that you were happily building a business process model when you encountered a situation where you had to model complex decision-making logic and made the mistake of starting to draw business process models filled with decision diamonds.

It shouldn't have taken you too long to realize that BPMN models aren't a great fit for modeling these complex decisions. Hopefully, you discovered decision tables. Decision tables are great at identifying all of the factors that go into making a business decision, and describing the logic involved in decision-making; but decision tables alone don't capture everything required to define decision logic. Where can you find a model that helps you link business processes, decision tables, inputs, requirements, and more?

That's where DMN comes in. It defines a standard notation for decision models, decision trees, decision expression language, and the new decision requirements diagram (DRD) – yes, another three-letter acronym. This decision requirements diagram is a new model for linking together all of the elements that are involved in decision-making.

There's much more to it, but in a simple way, a DRD is primarily comprised of these elements:

  • Decisions
  • Input data
  • Knowledge sources
  • Business knowledge models (which represent things like business rules and decision tables)

The DRD identifies all of the elements involved in a set of decisions and the relationships between them.

Notice that DMN doesn't replace existing standard modeling notation – it is designed to be used alongside BPMN models, business rules, and other deliverables. In fact, the DRD is really designed to define relationships between many of these other models and business decision logic.

DMN is currently in a beta phase, and a final specification could possibly be available before the end of 2014. You can find the current version of the specification here: http://www.omg.org/spec/DMN/.

Some of the content of the specification is simple and straightforward, while other portions of the specification contain detailed technicality. For an introduction to the standard, I'd suggest jumping to chapter five, which provides an introduction to DMN, then reading the first half of chapter six, the first half of chapter eight, and the DMN example described in chapter eleven.

During your first time, you might consider skipping over the “metamodel” sections – they are likely to give you a headache if you look at them too early. Also, the chapters about the standard expression language, FEEL and S-FEEL, essentially contain technical reference information. FEEL is the “friendly-enough-expression-language” that can be used to define the logic used within a decision. S-FEEL is a simplified subset of FEEL. These chapters are great for reference, but they don't provide edge-of-your-seat reading experiences.

Take some time to selectively read through the specification and think about how you might be able to use some of these standard models for describing decision logic on your project. If you've been using any type of flowcharts to model decision logic, then take a serious look at starting with decision tables and working your way up to decision requirements diagrams.

Topics: Business Analysis, Methodologies

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