Spare Parts Shop ERD models a multi-currency invoicing system with inventory management, employee authentication, and line-item tracking across Categories, Goods, Employees, Invoices, and Invoice_Items tables. Data flows from Categories through Goods to Invoice_Items, with Employees linked to Invoices and optional Technician references, supporting SAR and YER currency conversions. This schema demonstrates normalized relational design for retail operations handling stock quantities, cost tracking, profit margins, and exchange rate snapshots at transaction time. Fork and customize this ERD on Diagrams.so to adapt it for your spare parts, automotive, or equipment rental business. The optional Technician_ID field and computed Final_Total_YER showcase real-world complexity in multi-currency, service-inclusive invoicing.