What is a use case vs use case diagram?

Question

Accepted Answer

**Use case** — detailed description. **Use case diagram** — visual overview.

**Use case:**
- Detailed text.
- Steps and flows.
- Preconditions.
- Postconditions.

**Use case diagram:**
- Visual representation.
- Actors and use cases.
- Relationships.
- System boundary.

**Example:**
```
Use Case Diagram:
[Customer] ---- (Login)
     |              |
     +--- (Browse)
     |              |
     +--- (Purchase)

Use Case (Purchase):
Precondition: User logged in
Steps:
1. Add items to cart
2. Enter shipping info
3. Enter payment info
4. Confirm order
Postcondition: Order created
```

**Key differences:**
- **Diagram** — visual, high-level.
- **Use case** — detailed, textual.

Business Analyst: What is a use case vs use case diagram?