Relational Data Modeling

An entity is a thing the business needs to remember (customer, order, room); an attribute is a fact about it. Strong entities have their own identity, weak entities only exist inside a parent. Attributes can be simple, composite, derived, or multivalued, and each kind maps to tables differently.

8 min 1 code practice

Relationships connect entities: one-to-one, one-to-many and many-to-many, each with a cardinality (how many) and optionality (must there be one?). One-to-many is a foreign key on the "many" side; many-to-many needs an associative table; self-referencing relationships model hierarchies and graphs.

9 min 1 diagram 1 code practice

ER diagrams show entities, attributes and relationship cardinalities in crow's-foot notation, and they're the fastest way to agree on a model. When entities share a base (payment → card, UPI, wallet), choose single-table, class-table (joined) or concrete-table inheritance based on how often you query across subtypes.

8 min 1 diagram 1 code practice

Three worked models that exercise every relationship type: a library (copies vs titles, loans over time), flight booking (flights vs scheduled departures, seats, passengers per booking), and ride sharing (riders, drivers, vehicles, trips with state).

8 min 1 diagram 1 code practice