Entity-relationship diagram for a unified rental and retail sales platform with separate transaction flows for purchases and time-based rentals. Customers and users interact with products through Sales_Transaction and Rental_Transaction entities, each with detailed line items and flexible payment tracking. The schema supports inventory management across both sales and rental channels, with category-based product organization and comprehensive audit trails via created_at timestamps. Fork this ERD on Diagrams.so to customize for your business logic, add constraints, or export as SQL DDL. The Payment entity's optional foreign keys elegantly handle both transaction types while maintaining referential integrity.