Extensions

Extensions

The CDM is extensible without forking, following the OCDS extension pattern. Extensions let domains elaborate the model (e.g. defence procurement, construction) while keeping the core lean.

What an extension is

An extension is a published, versioned package that adds object types, fields, or codelist values under its own namespace (specification §11.1).

The rules

1. Add, don't change. Extensions MUST NOT redefine or remove core fields. They only add new structure under their own namespace.
2. Promotion path. Community extensions MAY be submitted to Concert for review and, if broadly useful, promoted into the core model through the change-control process. This keeps the core lean while allowing domain-specific elaboration.
3. Separate conformance. Core conformance is assessed against the core model only; extensions are conformance-assessed separately.

Proposing an extension

Per CONTRIBUTING.md, extensions that add (rather than change) structure should be proposed as packages under an /extensions path. The general flow:

1. Open an issue describing the gap the extension fills.
2. Define the new object types / fields / codelist values under a dedicated namespace.
3. Provide at least one example instance and the schema additions.
4. Submit a pull request; CI must pass.

See Contributing and Governance & Versioning.

Relationship to the agent layer

Note that the Agent Layer is not an extension — it is core, SIGNET's original contribution. Extensions are for additional domain structure on top of the core four-layer model.