What must the relationship between OrderItem and Product be based on?

The relationship between OrderItem and Product is fundamentally based on both the CompanyID and ProductID columns. This is because each product is typically associated not just with its own unique identifier (ProductID) but also with a specific company (CompanyID) that manufactures or sells the product.

In a relational database, to ensure data integrity and meaningful relationships, it is essential to use identifiers that capture the full context of the entities involved. The combination of CompanyID and ProductID provides a unique reference for a product within the scope of a particular company, allowing for accurate tracking of orders and inventory. This is particularly important in databases where products may overlap across different companies, ensuring that there is no ambiguity when linking order items to their corresponding products.

Using just the ProductID might lead to confusion if the same product ID exists under multiple companies. Therefore, opting for both columns is critical to establishing a robust and unambiguous relationship in the database design between OrderItem and Product.