Database Schema Design (SQL/NoSQL)

Act as a database architect. Design a database for: [APPLICATION_DESCRIPTION]. Provide: Entity Relationship Diagram (ERD) with entities, attributes, relationships (1:1, 1:N, N:N), SQL schema (CREATE TABLE statements with primary keys, foreign keys, indexes, constraints), NoSQL schema (document structure for MongoDB/Firestore), Sample queries (SELECT, INSERT, UPDATE, DELETE with joins), Query optimization (EXPLAIN plan analysis), Backup and recovery strategy, and Database migration plan.