research: Wikibase/Wikidata deep dive (entity-statement graph, SPARQL); UC-73-75

SHARD-WP-0003 T2. Structure & native-query far-end: typed knowledge graph
(items/properties, statements = claim+qualifiers+references+rank), RDF
projection + SPARQL (WDQS/Blazegraph) incl. federated SERVICE, opaque stable
Q/P identity (labels-as-annotation), statement-level provenance. UC-73
(typed-graph shard, lossy render), UC-74 (SPARQL + federated query), UC-75
(per-assertion provenance). Enriched UC-34/58/52/24. Marks T2 done.
Feeds SHARD-WP-0002 T12/T16.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

research/260614-wikibase-deep-dive/README.md

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+# 260614 — Wikibase / Wikidata deep dive
+
+Deep dive on **Wikibase** (the MediaWiki extension behind **Wikidata**) as the
+**entity-statement (RDF) far end** of the structure and native-query spectra: items and
+properties, statements = claim + qualifiers + references + rank, stable opaque IDs, and
+**SPARQL** (Wikidata Query Service / Blazegraph) including **federated** queries.
+
+- `findings.md` — data model, RDF/SPARQL surface, storage & history, capability profile,
+  INTENT mapping, UC seeds (UC-73–UC-75), architecture notes for SHARD-WP-0002, open
+  questions, sources, traceability.
+
+Catalog yield: UC-73 (attach a typed entity-statement / RDF shard, lossy render to a page),
+UC-74 (graph query the union via SPARQL + federated `SERVICE` cross-endpoint query), UC-75
+(statement-level provenance — references + rank per assertion). Enriched UC-34/58/52/24.
+Feeds SHARD-WP-0002 T12 (structured/typed page model) and T16 (stable language-neutral
+identity ≠ label/placement).