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Why DMN? (In 1000 Words)

Blog: Lux Magi – Decision Management for Finance Blog

At the time of writing there are two major industry standards for modelling business decisions: The Decision Model (TDM) defined by Sapiens Inc, established in 2009 and documented in The TDM book by Larry Goldberg and Barbara von Halle and The Decision Model and Notation (DMN) an open standard defined by the Object Management Group (OMG) in 2014 and version 1.1 is due to ratified later this year.

In this article we explain why, given the choice, you should model your business decisions using DMN as opposed to any other notation. Decision modelers should understand how TDM and DMN are similar, how they differ and their comparative strengths and weaknesses.

A Few Words About Decision Modelling Notations

Once you accept the benefits of Decision Management and Decision Modelling you will know what Business Decisions are and the need to use a single notation, across your enterprise, to model them. Using a single, defined notation allows your models to be unambiguously understood, and shared, among distributed teams of business analysts. It increases the effectiveness of team collaboration and avoids misunderstandings. It allows consumers of Decision Models to focus on the underlying meaning of decisions and their accuracy—free from the need to understand the vagaries of each analyst’s preferred notation.

Why Use an Industry Standard Notation?

Industry standard notations have been designed and refined to maximise their effectiveness by many expert practitioners over years. The same cannot be said of a home grown notation. Furthermore, well designed notations can improve the integrity of business logic by exposing contradictions and gaps. Use of industry standards also make it easier to procure expert help from the marketplace.

Why Use DMN?

It’s an Open Standard

DMN is an open standard which means it is not, like TDM, owned by a specific vendor or subject to restricted distribution. DMN is defined, ratified and freely published by the Object Management Group (OMG). The Object Management Group Inc. is an international, not-for-profit, technology standards consortium specializing in the development and custodianship of standard notations used by businesses in over twenty market verticals.

A full definition of TDM is reserved only for clients of Sapiens Inc and the only full implementation of TDM is their DECISION toolset (we discount superficial implementations like Visio templates). DMN (according to the DMN Tool Catalog) is supported by twelve toolsets (as of January 2016) and more are planned. The OMG ensure that the definition of the standard is available to all and this promotes competition.

It’s Built by Many Experienced Practitioners

OMG are also responsible for, among others, three world dominant standards for data, business process and model driven architecture modelling: UML, BPMN and MDA. The vendor team behind DMN includes Decision Management Solutions, Fair Isaac Corporation (FICO), IBM, Knowledge Partners International, Oracle and TIBCO Software Inc. This represents a enormous amount of collective experience in Decision Modelling. and standards administration.

TDM counters this partially by providing a modelling method, structural and integrity principles and best practices (which DMN lacks as it is merely a notation). However these can all be applied to DMN.

It is Evolving

DMN was first made available as a beta draft in early 2014, version 1.1 is shortly to be ratified by the OMG and new versions will follow. There are number of web materials and a book on the integration of business process and decision modelling. In contrast the public definition of TDM has changed little since 2010.

DMN Has a Richer Set of Features

DMN Decision Requirements Diagram

Like TDM, DMN models have two views: the Decision Requirements Diagram (DRD), depicting the structural dependencies of decisions, and the Decision Logic Diagram (DLD), defining decision logic in detail.

The TDM structural view only depicts the dependency of decisions on sub-decisions (rule families), the DMN DRD depicts these but also includes dependencies on: Input Data nodes which depict the sources of information; Knowledge Sources, or authorities, which are references to external business know-how, best practices, analytical models or compliance documents and Business Knowledge Models, a reusable element of business logic.

Both DMN and TDM define decision logic using decision tables. However DMN has many unique options that TDM does not offer:

Representation of logic in many other formats such as text, decision flows, decision trees or a PMML analytic models.

DMN Decision Table
Depict each rule as a row (as in the example), or a column or even in a crosstab.
Specify a Hit Policy which determines the number of rules that may be satisfied simultaneously against one datum, the number of conclusions that can be generated, how these are ordered and—where multiple rows are eligible but only one result is required—how an outcome is selected.
Support aggregation to yield one outcome from multiple satisfied rules.
Support validation by constraining the values of specified columns.

DMN has Solid Foundations

All expressions and values in DMN are underpinned by an algebraic expression language (the ‘Friendly Enough Expression Language’—FEEL). FEEL is used for calculations and expressing conditions. It is powerful, has a well defined syntax and a rich set of types. TDM lacks this foundation and users of this notation are limited to using simple values or defining their own expression syntax which undermines the value of using a standard notation.

The Future

TDM is a closed standard, defined and exclusively owned by Sapiens Inc. Many aspects of TDM have not been formally published and are embodied only in privately available white papers and in the Sapiens DECISION product. Other TDM tools exist, but as the owner of TDM is a tool vendor, a two-tier support model has evolved. TDM does not appear to be evolving.

DMN is a relatively new open standard, rigidly defined by a widely circulated, publicly available specification. At least twelve vendors are currently working on tool support. Although little experience of using DMN exists in the market at the time of writing, it is very likely that this is where the bulk of future innovation and vendor support will lie in the coming years.