ER Modeling and Relationship Cardinality

After normalization, interviewers test whether you can turn requirements into a schema. The prompt is usually open-ended: "Design a database for a ride-sharing app" or "Model a library system."

This is an entity-relationship (ER) modeling exercise. They are watching how you identify entities, attributes, and the relationships between them, including cardinality.

The skill is converting English nouns and verbs into tables and foreign keys.

Three building blocks form every ER model:

• Entity: a thing you store data about (Customer, Order, Product). Usually becomes a table.
• Attribute: a property of an entity (name, price, created_at). Usually becomes a column.
• Relationship: how entities connect (a Customer places an Order). Implemented with foreign keys or junction tables.

Tip from the prompt: nouns become entities/attributes, verbs become relationships.