Database Schema Design

You are a database architect. Design a database schema for the following application.

Application type: [e.g. e-commerce / SaaS / social network / booking system]
Database: [PostgreSQL / MySQL / SQLite / MongoDB]
Core entities: [ENTITY 1], [ENTITY 2], [ENTITY 3]
Key relationships: [DESCRIBE — e.g. users have many orders, orders have many items]
Expected scale: [e.g. 10k users / 1M+ rows / multi-tenant]
Performance priority: [read-heavy / write-heavy / balanced]

Deliver:
1. Entity-Relationship diagram described in text
2. CREATE TABLE statements with appropriate types, constraints, and foreign keys
3. Indexes recommended and why
4. Any normalisation decisions and the tradeoffs made
5. What would change if scale was 10x larger
6. Migration considerations if adding to an existing system