# What is DMN?

DMN (Decision Model and Notation) allows you to create decision tables for evaluating results based on given inputs. It offers a graphical representation of decision-making logic that is easily understandable.

### Decision Requirements Diagram (DRD)

- At the top level, DMN uses a Decision Requirements Diagram (DRD) to represent the structure of decisions and their dependencies.
- The DRD consists of nodes representing decisions, input data, and knowledge sources, connected by arrows indicating the relationships between them.

### Decision Tables

- A decision table is a fundamental component of DMN, used to model decision logic.
- Decision tables consist of columns representing input variables, output variables, and decision rules.
- Each row in a decision table represents a combination of inputs and specifies the corresponding output or decision to be made.

### Input Data

- Input data represents the information or data elements that are required for making decisions.
- Input data elements are often represented as external to the decision logic itself, and their values are provided as input when evaluating decisions.

### Decision Logic

- DMN provides various constructs to represent decision logic, including decision tables, business knowledge models, and decision trees.
- Decision logic defines the rules or conditions based on which decisions are made.

### Output Expressions

- DMN allows the definition of output expressions within decision models, which specify how output results should be calculated based on input data.
- Output expressions can use various constructs such as mathematical expressions, text concatenation, or logical operations to determine the output result.

### Decision Results

- Once a decision model is evaluated based on the provided input data and decision logic, it produces a decision result, which includes the output result(s) of the decision(s) made.
- The decision result represents the final outcome or decision produced by the decision model.