Database Schema Designer

Design a relational database schema for [APPLICATION TYPE — e.g. e-commerce platform, SaaS app, social network]. Core features: [LIST 3–5 MAIN FEATURES]. Database: [PostgreSQL/MySQL/SQLite]. For each table, provide: (1) table name and purpose, (2) all columns with data type, constraints (PRIMARY KEY, NOT NULL, UNIQUE, DEFAULT), and a brief description, (3) foreign key relationships and the relationship type (one-to-one, one-to-many, many-to-many). After the schema, provide: the CREATE TABLE SQL statements in order of dependency, 2–3 example indexes to add for query performance, and one data integrity challenge to watch out for in this design.