A data model includes a products table and a sales table. A relationship is created between them. Which cardinality should be set to achieve an optimal model?

• A. One-to-one
• B. One-to-many
• C. Many-to-many
• D. None of the above

Answer: (B)

Understanding how cardinality works in a relational model helps you design a clean link between products and sales. A product is a unique item that can appear in many separate sales records, while each individual sale typically references a single product. This means the natural relationship is one product to many sales: one product can be found in many sales rows, but each sales row relates to only one product.

A one-to-one relationship would imply each product is sold in only a single transaction, which doesn’t reflect real-world behavior. A many-to-many relationship would be used if a single sale could involve multiple products and each product could appear in many different sales, which is common in practice but is usually modeled with a separate line-item or junction table to connect sales to products. Given a straightforward link where every sale references one product, the one-to-many setup is the appropriate choice.