ADR-009: SPARQL is external federation only — CUE comprehensions are the query layer

Field	Value
Status	accepted
Date	2026-02-18

Context

Docs framed SPARQL as a primary query mechanism. This misrepresents the architecture.

Decision

SPARQL is for external federation only. Inside CUE, comprehensions ARE the query layer.

Rationale

CUE unification IS a query engine for the closed world. SPARQL adds runtime dependency that doesn't exist.

Consequences

• Oxigraph reclassified from 'optional infrastructure' to 'external federation only'
• Docs distinguish 'inside CUE' (comprehensions) from 'outside CUE' (SPARQL/triplestore)
• Profile README no longer implies SPARQL is the primary query method