ADR 0004 — All validation in SHACL, never OWL/RDFS

Status: accepted
Date: 2026-06-21

Context

Ratings have hard rules: a star value must be in [1,5], a thumb must be 0 or 1, a body is required, a comment must be a non-empty string. These are closed-world, rejecting constraints. RDFS/OWL are the wrong tool: they are open-world and monotonic — they infer rather than reject. Asserting ratingValue 7 against an OWL bound does not fail; it just adds a triple.

Decision

Structure (subclass, motivation relations) lives in ontology/freedback.ttl (RDFS/OWL).
All validation (datatype, bounds, required, reject) lives in ontology/shapes.ttl as SHACL Core. The feedback-server runs it on write, before persistence; invalid bodies are rejected 422 with the SHACL report.
Engine: rudof shacl_validation (native). Shapes are loaded once at boot.
The profile is pinned per-annotation via dcterms:conformsTo (https://freedback.net/profile/1).

SHACL Core, not SHACL-SPARQL

We restrict to SHACL Core so any conformant validator agrees with rudof and the constraints stay declarative. Consequence: bounds are validated against the default scales (stars 1..5, scalar 0..1, thumb {0,1}). Validating a custom scale (ratingValue between the body's own worstRating/bestRating) needs a sibling-property comparison that Core cannot express; that is a future profile (tracked as an issue), not a reason to leak validation into code.

WASM

The shacl_validation/json-ld/oxigraph stack is native-first. WASM clients do not validate locally; they ship pre-compacted payloads using the pinned @context and rely on the server to validate on write. This matches the plan's portability fallback and keeps the browser bundle small. protocol-lib exposes SHACL only under the shacl feature (off for default-features = false).

Consequences

There is exactly one place to change a rule: shapes.ttl. Code never encodes bounds. Annotation::structural_check only guards un-processable input (e.g. empty body) — it is a convenience, not the authority.
The validation report returned to clients is the SHACL report, so clients get machine-readable, profile-anchored errors.