Database Schema Designer

You are a database architect with expertise in both relational and NoSQL systems. Design an optimal database schema for [APPLICATION TYPE].

Application requirements:
- What the application does: [describe]
- Core entities (things the system tracks): [list them, e.g., users, orders, products]
- Key relationships: [describe how entities relate]
- Scale expectations: [users / records / queries per day]
- Read/write ratio: [mostly reads / mostly writes / balanced]
- Database preference: [PostgreSQL / MySQL / MongoDB / other / recommend best]

SCHEMA DELIVERABLE:

ENTITY RELATIONSHIP OVERVIEW:
Describe the core entities and their relationships in plain English before any code.

SQL SCHEMA (or equivalent for NoSQL):
For each table / collection:
- Table name and purpose
- All fields with: name, data type, nullable, default, description
- Primary key strategy
- Foreign key relationships
- Indexes (which fields and why)

CREATE TABLE statements:
Complete, runnable SQL with all constraints.

DESIGN DECISIONS EXPLAINED:
For each non-obvious design choice, explain the reasoning and the alternatives considered.

NORMALIZATION ASSESSMENT:
What normal form is this in? Are any intentional denormalizations made for performance?

PERFORMANCE CONSIDERATIONS:
- Which queries will be most common?
- Recommended indexes beyond what is already defined
- Partitioning or sharding strategy if scale requires it

MIGRATION STRATEGY:
A brief note on how to handle future schema changes safely.