Use case diagrams in Software Engineering - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a use case diagram?

A use case diagram is a simple visual tool that shows how users (called actors) interact with a system to achieve goals. It helps understand what the system does from the user's perspective.

beginner

Who or what is an actor in a use case diagram?

An actor represents a user or another system that interacts with the system being designed. Actors are outside the system and show who uses the system's functions.

beginner

What does an oval shape represent in a use case diagram?

An oval represents a use case, which is a specific function or goal that the system performs for an actor.

intermediate

Why are use case diagrams useful in software development?

They help teams understand user needs clearly, communicate system functions simply, and plan what the system should do before building it.

intermediate

What is the difference between 'include' and 'extend' relationships in use case diagrams?

Include means one use case always uses another as part of its process. Extend means one use case adds optional or conditional behavior to another.

In a use case diagram, what does an actor represent?

A A user or external system interacting with the system

B A function inside the system

C A database storing information

D A software developer

Actors are users or external systems that interact with the system to achieve goals.

Which shape is used to represent a use case in a use case diagram?

A Rectangle

B Oval

C Triangle

D Diamond

Use cases are shown as ovals to represent system functions or goals.

What does an 'include' relationship mean in a use case diagram?

A One use case always uses another as part of its process

B A use case is replaced by another

C Two actors communicate directly

D One use case optionally adds behavior to another

'Include' means a use case always calls another use case as part of its steps.

Why are use case diagrams helpful before coding a system?

A They design the database schema

B They show detailed code logic

C They replace testing

D They help understand user needs and system functions clearly

Use case diagrams help clarify what users want and what the system should do.

Which of the following is NOT typically shown in a use case diagram?

A Actors

B Use cases

C Detailed user interface design

D System boundaries

Use case diagrams focus on interactions and goals, not detailed screen designs.

Explain what a use case diagram is and why it is important in software development.

Think about how it shows users and system functions visually.

Describe the difference between 'include' and 'extend' relationships in use case diagrams with examples.

Consider when one function always happens versus when it happens only sometimes.

Practice

1. What is the main purpose of a use case diagram in software engineering?

easy

A. To test the software performance

B. To design the database schema

C. To write the program code

D. To show users and their interactions with system functions

Solution

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

   Use case diagrams visually represent how users (actors) interact with the system's functions (use cases).

2. Step 2: Compare with other software tasks

   Designing databases, coding, and testing are different activities not shown by use case diagrams.

3. Final Answer:

   To show users and their interactions with system functions -> Option D

4. Quick Check:

   Use case diagrams = show actors and interactions [OK]

Hint: Use case diagrams focus on users and their actions [OK]

Common Mistakes:

• Confusing use case diagrams with database design
• Thinking use case diagrams show code details
• Assuming use case diagrams test software

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

easy

A. A stick figure

B. A rectangle

C. An oval

D. A diamond

Solution

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

   Actors are represented by stick figures to symbolize users or external systems.

2. Step 2: Recognize other symbols

   Ovals represent use cases, rectangles and diamonds are not used for actors.

3. Final Answer:

   A stick figure -> Option A

4. Quick Check:

   Actor symbol = stick figure [OK]

Hint: Actors are stick figures in use case diagrams [OK]

Common Mistakes:

• Confusing actors with use cases (ovals)
• Choosing rectangles or diamonds for actors
• Not recognizing standard UML symbols

3. Consider a use case diagram with an actor "Customer" connected to two use cases: "Place Order" and "Track Order". What does this connection represent?

medium

A. Customer is a system component

B. Customer can perform both placing and tracking orders

C. Use cases depend on each other

D. Customer is a database entity

Solution

1. Step 1: Understand actor-use case connections

   Lines between an actor and use cases show the actor can perform those actions.

2. Step 2: Interpret the given connections

   Customer connected to "Place Order" and "Track Order" means the customer can do both activities.

3. Final Answer:

   Customer can perform both placing and tracking orders -> Option B

4. Quick Check:

   Actor connected to use cases = actor performs those actions [OK]

Hint: Lines show actor's possible actions [OK]

Common Mistakes:

• Thinking actors are system parts
• Assuming use cases depend on each other
• Confusing actors with database entities

4. A use case diagram shows an actor connected to a use case with a dashed arrow labeled "<<include>>". What is the likely issue if the arrow is drawn as a solid line instead?

medium

A. The diagram incorrectly shows a direct association instead of an include relationship

B. The actor symbol is wrong

C. The use case should be a rectangle

D. The diagram is missing actors

Solution

1. Step 1: Understand <<include>> notation

   The <<include>> relationship is shown with a dashed arrow from one use case to another, not from actor to use case.

2. Step 2: Identify the error in arrow style

   A solid line from actor to use case shows direct association, not an include relationship, so the diagram is incorrect.

3. Final Answer:

   The diagram incorrectly shows a direct association instead of an include relationship -> Option A

4. Quick Check:

   Include = dashed arrow between use cases, not solid actor line [OK]

Hint: <<include>> uses dashed arrows between use cases only [OK]

Common Mistakes:

• Drawing solid lines for <<include>>
• Confusing actor symbols with use case symbols
• Misplacing <<include>> arrows from actors

5. You want to model a system where a "User" can either "Login" or "Register" before accessing "Dashboard". Which use case diagram structure correctly shows that "Dashboard" use case requires either "Login" or "Register" first?

hard

A. "Login" and "Register" use cases extend "Dashboard" use case

B. "Dashboard" use case extends "Login" and "Register" use cases

C. "Dashboard" use case includes both "Login" and "Register" use cases

D. Login" and "Register" use cases are actors

Solution

1. Step 1: Understand include vs extend relationships

   Include means mandatory sub-function; extend means optional or conditional addition.

2. Step 2: Model login/register before dashboard

   Since "Dashboard" requires either "Login" or "Register" first, "Dashboard" use case includes both "Login" and "Register" use cases to show mandatory preconditions.

3. Final Answer:

   "Dashboard" use case includes both "Login" and "Register" use cases -> Option C

4. Quick Check:

   Include = mandatory use case inclusion [OK]

Hint: Use include for mandatory preconditions before main use case [OK]

Common Mistakes:

• Using extend instead of include for mandatory steps
• Confusing actors with use cases
• Reversing direction of include/extend arrows