0054: Implementer declaration requiredness

Extend ADR 0053: Implementer revision comparison to classify declaration obligations for corresponding groupings. An existing implementation satisfying the earlier model may omit an optional declaration. Making that declaration mandatory can therefore require work, even when some implementations already provide it. Releasing an obligation still permits its representation and is compatible for implementers.

Compare each Thing and Object’s resolved mandatory closure after composition, restricted to declarations present at corresponding document, class and Given Name paths in both revisions. Any new obligation is breaking for implementers, including when other obligations are released. Released obligations alone are compatible. Equal sets produce no requiredness difference. Client comparison remains the default and retains its existing rule that a released obligation is breaking. These are Esdieff compatibility policies derived from the selected perspective. RFC 9880 Section 4.5 supplies the declaration relationships, not these classifications.

Reuse the relationships of ADR 0026: Required declaration relationships and source evidence and effective coordinates of ADR 0036: Copied reference relocation. The closure includes enclosing groupings needed to represent a nested target and requirements of mandatory groupings. A child requirement in an optional grouping applies whenever that grouping is represented without making the outer grouping mandatory. Pointer, short-name and carrier forms are equivalent when they establish the same closure.

Added or removed declarations retain independent endpoint differences, which remain undetermined for implementers. Missing declarations do not establish optionality. Partial or unavailable resolution keeps the existing conservative scope and cause. It cannot prove a subset relation. Independent composition and data differences retain their own results. No data direction or JSON value witness is added to requiredness, which reports one changed sdfRequired quality per affected corresponding grouping.

Comparison contract esdieff.revision-comparison/6 supersedes /5. Diff envelope 1.7 and acknowledgement format 1 remain unchanged. An old undetermined acknowledgement does not match a newly classified difference. Authors must review intended differences and may need to regenerate acknowledgements. Property capabilities, grouping counts, whole Action/Event input/output presence and Context metadata compatibility retain their existing implementer boundaries.

Considered options

Reversing the final client classification would mark a simultaneous addition and release compatible for implementers. Instead, assess whether each side’s obligations entered or left the closure. Comparing authored lists would report changes between equivalent spellings and lose composed requirements. Treating an absent endpoint as optional would introduce an endpoint-presence policy outside this decision’s scope.