Add governed buildings register snapshot

docs/DATA_SPECIFICATION.md

@@ -61,22 +61,43 @@ GRB-gebouwpolygonen worden gebruikt als ground-truth proxy. Niet absoluut perfec
 
 ### Rol
 
-Aanvullende gebouwinformatie bij geometrieën.
+Authoritative register lifecycle and relation metadata attached to a dated
+building snapshot. It complements GRB; it does not replace the separate GRB
+footprint evidence or its QA role.
 
 ### Gebruik
 
-- gebouwmetadata
-- identificatie
-- status
-- koppeling met GRB-gebouwpolygonen indien mogelijk
+- stable building object and version identity
+- official lifecycle status and geometry method
+- aggregate registered building-unit counts by lifecycle status
+- aggregate address counts by register status
+- classified reconciliation against persisted GRB geometry
 
 ### Type
 
-Vector/API/metadata.
+Official OGC API Features input, normalized polygon GeoJSON upload and
+PostGIS `vector_features` output.
 
-### Prioriteit
+### Persisted contract
 
-V2 of V1.5.
+- `dataset_role=reference`
+- `source_name=digitaal_vlaanderen_buildings_addresses_register`
+- `reference_layer_name=building_registry`
+- `temporal_granularity=snapshot`
+- stable building identity within the register, but no fabricated historical
+  observation between snapshots
+- polygon geometry clipped in EPSG:31370 and persisted as EPSG:4326
+- selection metrics: exact footprint hectares, building lifecycle counts,
+  unit counts, address-status counts and confirmed GRB match counts
+
+### Privacy and semantics
+
+Queryable properties may contain register object ids, lifecycle status,
+geometry method, aggregate unit/address counts and GRB reconciliation evidence.
+They must not contain `VolledigAdres`, `Straatnaam`, `Huisnummer`,
+`HuisnummerLabel` or `Busnummer`. Address and unit counts may not be labelled
+as population, residents, households or dwellings. Building footprint is
+ground area, not floor area, height or volume.
 
 ## OpenStreetMap