“Major changes” / versioning policy / language consistency

[khaeru]

The README of this repository has a heading “SDMX 3.1.0 Major Changes”, and the draft document for “Section 1” includes a heading “2.4 Major Changes from 3.0 to 3.1.0”. At the same time, section “2.3 Major changes from 2.1 to 3.0” of the same document includes:

Versioning of Structural Metadata Artefacts

• Adoption of the three-number semantic versioning standard for structural metadata artefacts (https://semver.org/)

This addition reveals that there was no clear versioning standard or policy for SDMX per se. If it were semantic versioning, the change from SDMX 3.0.0 to 3.1.0 would be a "minor" change, and the SemVer standard says:

Given a version number MAJOR.MINOR.PATCH, increment the:

1. MAJOR version when you make incompatible API changes
2. MINOR version when you add functionality in a backward compatible manner
3. PATCH version when you make backward compatible bug fixes

This would imply that all changes in 3.1.0, such as "Data Constraint: Reference reversed" should be implemented in a "backward compatible manner"; something that is not addressed in the updated text of the documents in this repo.

Conversely, if this is indeed a backwards-incompatible/“major” change, then SemVer would require that the version number be incremented "4.0.0".

So it seems clear that SemVer is not in use for SDMX itself. It would be good to have a clear statement of the meaning of the different parts of the SDMX version number, and when and how they will be incremented.