Why this matters
- Entity identification is step two of the six-step framework — do it before APIs.
- Wrong ownership arrows cause every later refactor to hurt.
- Noun/verb extraction is a skill you can practise on any problem statement.
- Cardinality mistakes (1:1 vs 1:N) show up in almost every booking problem.
ParkingLotentry facade
ParkingFloorcollection of spots
Ticketissued on entry
Vehiclecar, bike, truck
ParkingSpot links Vehicle when occupied; Strategy picks spot by vehicle type.
Overview
Turn a problem statement into entities before you name a single method. Study each section below in order — every list is interview-ready reference material.
Noun extraction
Points to cover
- Definition — what Noun extraction means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
Verb mapping
Points to cover
- Definition — what Verb mapping means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
Cardinality
Points to cover
- Definition — what Cardinality means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
CampusOS parking example
Points to cover
- Definition — what CampusOS parking example means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
// CampusOS — apply "Noun extraction" on paper first, then in code
public final class EntityRelationshipThinkingExample {
// 1. Name entities from the problem statement
// 2. Draw relationships before writing methods
// 3. Introduce patterns only when a force appears
}
Quick recall
Everything you need if you only revisit this box.
- Noun extraction — review this slice before mock interviews.
- Verb mapping — review this slice before mock interviews.
- Cardinality — review this slice before mock interviews.
- CampusOS parking example — review this slice before mock interviews.
Test yourself
Answer these before moving on — recall is what makes it stick.