I am pleased to announce a new Decision Table Modeling online training offering taught by Professor Jan Vanthienen, a leading decision table expert. We are running a pilot of this class February 2-4 an you can get details, and a great price, here. To give you a taste of Jan’s approach, here’s a guest article by him.
The Value of Good Decision Table Modeling
By Jan Vanthienen, KU.Leuven
Managing and modeling decisions is crucial for business. The new DMN (Decision Model and Notation) standard emphasizes the importance of business decisions, and also offers a standard notation and expression for decision requirements and decision logic.
Decision tables look straightforward: a number of rows or columns containing decision rules about combinations of condition expressions with their respective outcome. The reason for their success is simply that every column or every row (depending on orientation) is about one specific condition. This fixed order of conditions allows a complete and easy overview of decision rules for a specific decision. It also allows grouping of related rules into tables, thereby providing an overview to a large number of decision rules.
The real advantage for business, however, is the ability to obtain consistency, completeness and correctness of the decision logic. Avoiding redundancy and overlapping rules is a key element in constructing and maintaining decision tables that offer true value for business.
Tables for Decision Logic Modeling
DMN provides constructs for both decision requirements and decision logic modeling. The requirements level allows for modeling and managing linked decisions, abstracting from the detailed logic of each decision. The decision logic level standardizes the way to express decision logic, e.g. in the form of decision tables. DMN provides a common model and notation that is readily understandable by all business users, from the business analysts needing to create initial decision requirements and then more detailed decision logic models, e.g. in the context of business processes, to the business people who will manage and monitor those decisions, and finally, to the developers responsible for implementing the decisions.
Decision logic modeling can take many forms, depending on the decision at hand, but decision tables are an important element. Most people know what decision tables look like: a number of rows or columns containing decision rules about combinations of condition expressions with their respective outcome. Decision tables have always been known for their ability to offer a compact, readable and manageable representation of decision logic. But many do not realize how the decision table concept has been refined throughout the years into a strict and powerful modeling technique (based on consistency by construction, normalization, completeness, correctness, etc.).
Decision Table Methodology
Different forms of decision tables exist in business practice, even under different names and with different semantics. What DMN offers is a standard notation and the ability to recognize and unambiguously interpret and exchange tables of rules in different forms. The core methodology to build sound decision tables is not part of DMN, but it still holds.
The decision table methodology offers:
- Guidelines for composing effective decision tables (form, structure, meaning, etc.).
- An overview of advantages and disadvantages of different types of decision tables (different hit policies).
- A simple eight step method to construct good decision tables, starting from the description of the decision and leading to compact, normalized and optimized decision tables.
- A sound decomposition of the decision structure.
- Best practices on obtaining completeness, consistency, readability, maintainability.
- A transition from the specification to design, implementation and maintenance.