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DocBook 5: The Definitive Guide by Richard L. Hamilton, Norman Walsh

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Backward Compatibility

Whether you’re just getting started with DocBook, or curating a collection of tens of thousands of DocBook documents, one question that you have to consider is how stable is DocBook? Will the documents that you write today still be useful tomorrow, or next year, or in the next century?

This question may seem particularly pertinent if you’re in the process of converting a collection of DocBook 4.x documents to DocBook V5.0 because we introduced a number of backward-incompatible changes in V5.0.

The DocBook Technical Committee understands that the community benefits from the long-term stability of the DocBook family of schemas. We also understand that DocBook must continue to adapt and change in order to remain relevant in a changing world.

All changes, and especially changes that are backward incompatible (changes that make a currently valid document no longer valid under a new version of the schema), have a cost associated with them. The technical committee must balance those costs against the need to remain responsive to the community’s desire to see DocBook grow to cover the new use cases that inevitably arise in documentation.

With that in mind, the DocBook Technical Committee has adopted the following policy on backward-incompatible changes. This policy spells out when backward-incompatible changes can occur and how much notice the technical committee must provide before adopting a schema that is backward incompatible with the current release.

This policy allows DocBook to continue to change and adapt while simultaneously guaranteeing that existing users will have sufficient advance notice to develop reasonable migration plans.

With respect to schema changes, the technical committee asserts that the following points will always apply:

  • A point release (X.1 to X.2, X.2 to X.3, X.1 to X.1.2, etc.) will not contain any backward-incompatible changes.

  • A major release (X.1 to Y.0, X.2 to Y.0, X.1.2 to Y.0, etc.) may contain backward-incompatible changes if:

    • the change was announced in the release notes for the previous version (major or minor) and

    • the change was announced in a release that occurred at least six months previously.

By these rules, the technical committee can announce, in V5.1, for example, its plans to make a backward-incompatible change in V6.0. Then, in V6.0, if it’s been at least six months since V5.1 was released, it can make that change.

As a general rule, the technical committee tries to avoid backward-incompatible changes.

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