n8n-nodes-dmn

This is an n8n community node that allows you to use Decision Model and Notation (DMN) tables within your n8n workflows.

This node dynamically constructs and evaluates DMN 1.1 decision tables based on rules and data provided as inputs, leveraging the S-FEEL expression language subset supported by the underlying evaluation engine.

• DMN is an OMG standard for modeling and executing operational decisions.
• n8n is a fair-code licensed workflow automation platform.

Installation

Follow the installation guide in the n8n community nodes documentation.

Operation: Evaluate Decision

Executes a dynamically generated DMN decision table against input data.

• Inputs:
  1. Rules: An array of n8n items, where each item's JSON represents a single rule (row) in the decision table.
  2. Data: An array of n8n items, where each item's JSON represents the input context data to be evaluated against the rules.
• Output: Returns the decision result(s) merged with the original input data item, formatted according to the selected "Output Format" property.

Configuration

The node requires configuration through its properties:

• Input Parameters: Define the input columns used in the decision table and their data types. The names must match keys in the input Data items.
  • Supported Types: String, Number, Boolean.
• Output Parameters: Define the output columns produced by the decision table and their data types.
  • Supported Types: String, Number, Boolean.
• Hit Policy: Select the DMN hit policy to determine how multiple matching rules are handled.
  • Supported Policies: UNIQUE, FIRST, RULE ORDER, COLLECT.
• Output Format: Choose how the results are structured in the output items.
  • Formats: Row with all hits (always lists), Row with all hits (single items and lists), Row for each hit, JSON with Output.

S-FEEL Expressions

Input and output entries within the Rules data can utilize expressions based on the S-FEEL standard, as implemented by the underlying evaluation library. This includes:

• Comparisons (<, >, <=, >=)
• Ranges ([1..10], (1..10))
• Disjunctions (comma-separated lists like "a", "b", or 10, 20)
• Negation (not(...) - Note: For string negation, use <> "string" syntax in your rule input)
• Simple string literals ("go", "stay home")
• Numeric and boolean literals (10, true)
• The hyphen (-) for wildcard inputs.

Refer to the underlying library documentation for more specific S-FEEL details. Not all the features are 100% operational, so test your solution properly.

Resources

• n8n community nodes documentation
• OMG Decision Model and Notation (DMN) Specification v1.1
• dmn-eval-js Library (underlying engine)

Attribution

• This node leverages the dmn-eval-js library by Andre Hegerath.
• It is also based on the n8n community Nodes Starter template.

Disclaimer

Dynamically generating and evaluating DMN based on user inputs can be complex. While this node aims to support common use cases, edge cases or specific S-FEEL constructs might lead to unexpected behavior or parsing errors in the underlying library. Please test thoroughly and report any issues.

Prerequisites

You need the following installed on your development machine:

1. Set up git
2. Node.js and npm. Minimum version Node 18. You can find instructions on how to install both using nvm (Node Version Manager) for Linux, Mac, and WSL here. For Windows users, refer to Microsoft's guide to Install NodeJS on Windows.
3. Install n8n with:

npm install n8n -g

4. Import the lib from the settings panel

Recommended: follow n8n's guide to set up your development environment.

License

MIT