Reverse Engineering (reverse)

The reverse command converts an existing NodeSet2.xml file back into the OPC UA Modeler YAML DSL. This is the entry point for teams migrating from hand-written NodeSet XML files, or for importing third-party companion specification nodesets to use as a starting point.

opcua-modeler reverse --input MyModel.NodeSet2.xml --output my-model.yaml

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Why reverse-engineer?

Scenario	How reverse helps
You have existing NodeSet2.xml files and want to adopt the YAML workflow	Convert once, then maintain in YAML
You want to understand a companion specification (e.g., DI, Robotics)	Inspect it as readable YAML
You need to customise a third-party NodeSet	Import it, modify the YAML, regenerate

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Basic usage

# Reverse a single NodeSet2.xml to YAML
opcua-modeler reverse --input MyModel.NodeSet2.xml

# Specify output filename explicitly
opcua-modeler reverse --input MyModel.NodeSet2.xml --output my-model.yaml

By default, the output file is named after the input file with a .model.yaml suffix.

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What gets converted

The reverse command reconstructs:

• objectTypes — all custom ObjectType definitions
• variableTypes — all custom VariableType definitions
• dataTypes — enumerations and structure types
• referenceTypes — custom reference type definitions
• interfaces — OPC UA interface types
• instances — concrete object instances with placement references
• stateMachines — finite state machine definitions
• namespaces — imported namespace aliases (where known)
• promotedToMandatory — optional members that were instantiated
• Descriptions, display names, and engineering unit data

Fidelity

The reverse output is a good starting point but may require manual cleanup. Not all NodeSet2.xml constructs have a 1:1 YAML equivalent, and some legacy constructs (OPC UA 1.03 type dictionaries, BSD/XSD schemas) are deliberately omitted from the output.

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Round-trip workflow

A common workflow is to reverse-engineer once and then use generate for all subsequent changes:

NodeSet2.xml  ──reverse──►  model.yaml  ──generate──►  NodeSet2.xml (regenerated)
                                ▲
                           edit here

After the initial reverse, commit the .model.yaml to version control and treat it as the single source of truth. The original XML can be archived.

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Options

Flag	Short	Description
--input	-i	Input NodeSet2.xml file (required)
--output	-o	Output .model.yaml filename
--debug	-d	Extra debugging output