A model includes a products table and a table with monthly category targets; each product can belong to multiple categories and each category can have multiple products. Which cardinality should be set?

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

Answer: (C)

This question tests how to model relationships between entities in a relational database. When an entity in one table can be linked to many records in another, and the reverse is also true, you have a many-to-many relationship. Here, a product can belong to multiple categories and a category can contain multiple products, so the link between products and categories is many-to-many. Implementing that typically uses a junction table that stores pairs of product_id and category_id (and possibly extra attributes). The monthly targets table adds another dimension, but it doesn’t change the fact that the product–category link itself is many-to-many; it can be modeled alongside with its own tables as needed. Therefore, the appropriate cardinality is many-to-many.