ADR-0008 — A semantic model over standard vocabularies, English master

Status: Accepted (phase 1) · Date: 2026-09-29

Context

Photos are about more than albums: a class reunion, a family, a place, a part of life. A column per idea in DynamoDB would need a schema change for every new kind of event. The family works in three languages. DigitalHome.Cloud already models homes as a T-Box, SHACL shapes and per-tenant A-Boxes.

Decision

• Reuse before inventing. The model reuses:

  • schema.org for events, places and media objects
  • FOAF for persons, groups and depicts
  • the RELATIONSHIP vocabulary for family relations
  • SKOS for concept schemes
  • Web Annotation with media fragments for face regions (stored compactly on the Item, ADR-0009)
  • WGS84 for coordinates

  mt: adds only what these lack (mt:Item, mt:Family, mt:eventType, mt:lifeArea, mt:place, mt:classmateOf, mt:FaceAnnotation, …).

• Event types and life areas are SKOS concepts, so a new one is data. An "area" is two things: places (a hierarchy of mt:Place, optionally linked to GeoNames) and life areas (a SKOS scheme).

• English is the master. SHACL requires exactly one @en prefLabel per concept, and the tests require @de and @fr for everything a person sees.

• SHACL shapes define a valid A-Box. The tests are on the DHC pattern and prove the shapes refuse ten kinds of broken data, each for the right reason.

• A-Boxes are per family or occasion, and synchronised. They are edited on the edge or in the Mediathek, and synchronised through the edge's device token. That is phases 2 and 3, and not built yet.

Consequences

• A-Boxes are personal data. With sync (phase 3), family relations and attendance live in AWS too, behind Cognito and mt-admins. Face vectors still never leave the edge: an A-Box holds only confirmed names and photo regions.
• The site, the edge and later CLIP read labels from these files, so a new concept appears everywhere in three languages at once.
• Real A-Boxes never go into the repository, only fictional examples.