diff --git a/docs/architecture/c4-diagrams.md b/docs/architecture/c4-diagrams.md
index 9585f735..858082aa 100644
--- a/docs/architecture/c4-diagrams.md
+++ b/docs/architecture/c4-diagrams.md
@@ -572,3 +572,14 @@ sequenceDiagram
     Backend-->>Frontend: 200 OK — Document JSON
     Frontend-->>User: Refreshed document view
 ```
+
+---
+
+## Database
+
+Entity-relationship and full column reference for the PostgreSQL schema (30 tables, 7 domain groups). Source files in `docs/architecture/db/`.
+
+- **[db-relationships.puml](db/db-relationships.puml)** — Entity relationships: all tables and foreign-key connections, grouped by domain. Start here for an overview.
+- **[db-orm.puml](db/db-orm.puml)** — Full schema reference: all columns and types for all 30 tables. Use this when mapping Java entities to database columns.
+
+> Schema as of Flyway V60 (2026-05-06). Open in VS Code with the PlantUML extension (server: `http://heim-nas:8500`).