Use case diagrams in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to name the main actor in a use case diagram.

LLD

actor [1]

Drag options to blanks, or click blank then click option'

AUser

BSystem

CDatabase

DServer

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing system components like Server or Database as actors.

The main actor in a use case diagram is usually the User who interacts with the system.

2fill in blank

medium

Complete the code to define a use case named 'Login'.

LLD

usecase [1] as "Login"

Drag options to blanks, or click blank then click option'

AStart

BLogin

CUserLogin

DUC1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the descriptive name as the identifier.

Use cases are often labeled with identifiers like UC1 and given descriptive names.

3fill in blank

hard

Fix the error in the association between actor and use case.

LLD

actor User
usecase UC1 as "Login"
User [1] UC1

Drag options to blanks, or click blank then click option'

A--

B<->

C-->

D->

Attempts:

3 left

💡 Hint

Common Mistakes

Using arrows which imply direction.

In use case diagrams, associations between actors and use cases are shown with a simple line --.

4fill in blank

hard

Fill both blanks to show an include relationship from 'Register' to 'Validate User'.

LLD

usecase Register as "Register"
usecase ValidateUser as "Validate User"
Register [1] ValidateUser [2]

Drag options to blanks, or click blank then click option'

A<|--

B--

C<|..

D..>

Attempts:

3 left

💡 Hint

Common Mistakes

Using solid lines or wrong arrowheads for include.

The include relationship is shown with a dashed arrow <|.. pointing to the included use case.

5fill in blank

hard

Fill all three blanks to define an extend relationship from 'Make Payment' to 'Apply Discount' with condition '[if eligible]'.

LLD

usecase MakePayment as "Make Payment"
usecase ApplyDiscount as "Apply Discount"
MakePayment [1] ApplyDiscount [2] : [3]

Drag options to blanks, or click blank then click option'

A<|..

B..>

C[if eligible]

D--

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing include and extend arrows or missing the condition label.

The extend relationship uses a dashed arrow <|.. with a label showing the condition in square brackets.

Practice

1. What is the primary purpose of a use case diagram in system design?

easy

A. To show user roles and their interactions with the system

B. To display database table relationships

C. To illustrate the internal code structure

D. To list all system hardware components

Solution

1. Step 1: Understand the role of use case diagrams

   Use case diagrams focus on users (actors) and what they do with the system (use cases).

2. Step 2: Compare with other diagram types

   Database diagrams show tables, code diagrams show code structure, hardware diagrams show physical parts, none are use case diagrams.

3. Final Answer:

   To show user roles and their interactions with the system -> Option A

4. Quick Check:

   Use case diagram = user roles + actions [OK]

Hint: Use case = users + actions, not code or hardware [OK]

Common Mistakes:

• Confusing use case diagrams with class or sequence diagrams
• Thinking use case diagrams show database details
• Assuming use case diagrams show internal code logic

2. Which of the following is the correct symbol for an actor in a use case diagram?

easy

A. A rectangle with the actor's name inside

B. An oval shape showing a system function

C. A stick figure representing a user

D. A diamond shape indicating a decision

Solution

1. Step 1: Identify actor symbol in use case diagrams

   Actors are shown as stick figures to represent users or external systems.

2. Step 2: Differentiate other symbols

   Ovals represent use cases (functions), rectangles can be system boundaries, diamonds are for decisions in flowcharts, not use case diagrams.

3. Final Answer:

   A stick figure representing a user -> Option C

4. Quick Check:

   Actor symbol = stick figure [OK]

Hint: Actors are stick figures, use cases are ovals [OK]

Common Mistakes:

• Using rectangles for actors instead of stick figures
• Confusing use case ovals with actor symbols
• Mixing flowchart symbols with use case diagram symbols

3. Consider a use case diagram with actors Customer and Admin, and use cases Place Order, Cancel Order, and Update Inventory. Which use case should only be connected to the Admin actor?

medium

A. Place Order

B. Cancel Order

C. Place Order and Cancel Order

D. Update Inventory

Solution

1. Step 1: Analyze actor responsibilities

   Customers place and cancel orders; Admin manages inventory updates.

2. Step 2: Match use cases to actors

   Only Admin should connect to Update Inventory as it is a system management task.

3. Final Answer:

   Update Inventory -> Option D

4. Quick Check:

   Admin-only use case = Update Inventory [OK]

Hint: Admin manages system tasks, customers do orders [OK]

Common Mistakes:

• Connecting customers to inventory updates
• Assuming customers can update system data
• Linking all use cases to all actors

4. A use case diagram shows an actor connected to a use case with a dashed arrow labeled <<extend>>. What does this indicate?

medium

A. The extended use case adds optional behavior to the base use case

B. The actor is not allowed to perform the extended use case

C. The actor must always perform the extended use case

D. The use case is a system boundary

Solution

1. Step 1: Understand <<extend>> relationship

   The <<extend>> arrow shows optional or conditional behavior added to a base use case.

2. Step 2: Interpret actor connection meaning

   The actor can perform the base use case; the extended use case happens only sometimes.

3. Final Answer:

   The extended use case adds optional behavior to the base use case -> Option A

4. Quick Check:

   <<extend>> = optional behavior [OK]

Hint: <<extend>> means optional addition, not mandatory [OK]

Common Mistakes:

• Thinking <<extend>> means mandatory action
• Confusing <<extend>> with <<include>>
• Assuming <<extend>> defines system boundaries

5. You are designing a use case diagram for an online library system. Which of the following best represents a correct use case for the Member actor that includes an Admin actor managing the system?

hard

A. Member: Add Book, Remove Book; Admin: Borrow Book, Return Book

B. Member: Borrow Book, Return Book; Admin: Add Book, Remove Book

C. Member: Borrow Book, Add Book; Admin: Remove Book, Return Book

D. Member: Remove Book, Return Book; Admin: Borrow Book, Add Book

Solution

1. Step 1: Identify typical member actions

   Members usually borrow and return books, not manage inventory.

2. Step 2: Identify admin responsibilities

   Admins add or remove books to keep the library updated.

3. Step 3: Match actions to actors correctly

   Member: Borrow Book, Return Book; Admin: Add Book, Remove Book correctly assigns borrowing and returning to Member, and adding/removing to Admin.

4. Final Answer:

   Member: Borrow Book, Return Book; Admin: Add Book, Remove Book -> Option B

5. Quick Check:

   Member = borrow/return, Admin = add/remove [OK]

Hint: Members use books; Admins manage books [OK]

Common Mistakes:

• Swapping member and admin roles
• Assigning management tasks to members
• Mixing use cases between actors