Functional vs non-functional requirements in Software Engineering - Quick Revision & Key Differences

Recall & Review

beginner

What are functional requirements in software engineering?

Functional requirements describe what a system should do. They specify the tasks, functions, or behaviors the software must perform to meet user needs.

beginner

What are non-functional requirements?

Non-functional requirements define how a system performs its functions. They include qualities like speed, security, usability, and reliability.

beginner

Give an example of a functional requirement.

An example is: 'The system must allow users to log in using a username and password.' This describes a specific action the system must perform.

beginner

Give an example of a non-functional requirement.

An example is: 'The system should load the homepage within 2 seconds.' This describes a quality or performance measure, not a specific function.

intermediate

Why are non-functional requirements important?

They ensure the system is usable, reliable, and efficient. Without them, a system might work but be slow, insecure, or hard to use.

Which of the following is a functional requirement?

A The system must send an email notification when a user registers.

B The system should be available 99.9% of the time.

C The system must load pages within 3 seconds.

D The system should have a user-friendly interface.

Functional requirements describe specific actions or behaviors, like sending an email notification.

Non-functional requirements usually describe:

A What the system does.

B The programming language used.

C How the system performs.

D The number of users.

Non-functional requirements focus on qualities like performance, security, and usability.

Which is an example of a non-functional requirement?

A The system encrypts user data.

B Users can reset their password.

C The system must allow file uploads.

D Users can create profiles.

Encrypting data is a security quality, which is a non-functional requirement.

Functional requirements are important because they:

A Improve user satisfaction.

B Define system features and behaviors.

C Make the system secure.

D Ensure the system is fast.

Functional requirements specify what the system must do.

Which statement is true about non-functional requirements?

A They are the same as functional requirements.

B They are optional for software projects.

C They describe system functions.

D They include performance and reliability.

Non-functional requirements include qualities like performance and reliability.

Explain the difference between functional and non-functional requirements with examples.

Think about what the system does versus how well it does it.

Why are both functional and non-functional requirements important in software development?

Consider what happens if one type is missing.

Practice

1. Which of the following best describes a functional requirement in software engineering?

easy

A. The look and feel of the user interface

B. A measure of how fast the system responds

C. A feature that specifies what the system should do

D. The hardware needed to run the software

Solution

1. Step 1: Understand the definition of functional requirements

   Functional requirements describe specific behaviors or functions the system must perform.

2. Step 2: Match the option to the definition

   A feature that specifies what the system should do states a feature specifying what the system should do, which matches the definition.

3. Final Answer:

   A feature that specifies what the system should do -> Option C

4. Quick Check:

   Functional requirement = What system does [OK]

Hint: Functional = what system does, Non-functional = how it does [OK]

Common Mistakes:

• Confusing functional with non-functional requirements
• Thinking performance is a functional requirement
• Mixing hardware needs with software functions

2. Which of the following is an example of a non-functional requirement?

easy

A. The system must allow users to reset their password

B. The system should respond to user input within 2 seconds

C. The system must save user data to a database

D. The system must support login with username and password

Solution

1. Step 1: Identify non-functional requirements

   Non-functional requirements describe how the system performs, such as speed or reliability.

2. Step 2: Evaluate each option

   The system should respond to user input within 2 seconds specifies response time, which is a performance measure and thus non-functional.

3. Final Answer:

   The system should respond to user input within 2 seconds -> Option B

4. Quick Check:

   Non-functional = performance or behavior [OK]

Hint: Look for speed, usability, or reliability for non-functional [OK]

Common Mistakes:

• Choosing features as non-functional requirements
• Confusing functional actions with performance measures
• Ignoring timing or quality aspects

3. Consider this statement: "The system shall encrypt all user data before saving." What type of requirement is this?

medium

A. Functional requirement

B. Non-functional requirement

C. Neither functional nor non-functional

D. Both functional and non-functional

Solution

1. Step 1: Analyze the statement's action

   Encrypting data is a specific action the system must perform, describing what it does.

2. Step 2: Classify the requirement type

   Since it describes a function (encryption), it is a functional requirement.

3. Final Answer:

   Functional requirement -> Option A

4. Quick Check:

   Encryption = system function = functional [OK]

Hint: If it describes a system action, it's functional [OK]

Common Mistakes:

• Thinking encryption is a performance or quality aspect
• Confusing security features with non-functional requirements
• Selecting 'both' without clear reasoning

4. A software team wrote this requirement: "The system must be user-friendly." What is the main issue with this requirement?

medium

A. It describes a functional requirement incorrectly

B. It is a security requirement

C. It is a hardware requirement, not software

D. It is too vague and not measurable

Solution

1. Step 1: Understand the requirement's nature

   "User-friendly" describes a quality but is subjective and lacks clear criteria.

2. Step 2: Identify the problem

   Requirements must be clear and measurable; this one is vague and cannot be tested easily.

3. Final Answer:

   It is too vague and not measurable -> Option D

4. Quick Check:

   Good requirements = clear + measurable [OK]

Hint: Vague terms mean poor requirements [OK]

Common Mistakes:

• Assuming all non-functional requirements are clear
• Confusing vague qualities with functional features
• Ignoring measurability in requirements

5. A project requires the system to handle 1000 users simultaneously and respond within 1 second. Which combination correctly classifies these requirements?

hard

A. "Handle 1000 users simultaneously" is functional; "respond within 1 second" is non-functional

B. "Handle 1000 users simultaneously" is non-functional; "respond within 1 second" is functional

C. Both are functional requirements

D. Both are non-functional requirements

Solution

1. Step 1: Analyze "handle 1000 users simultaneously"

   This describes a specific system function to support multiple users at once, which is a functional requirement.

2. Step 2: Analyze "respond within 1 second"

   This describes a performance measure, how fast the system reacts, so it is non-functional.

3. Final Answer:

   "Handle 1000 users simultaneously" is functional; "respond within 1 second" is non-functional -> Option A

4. Quick Check:

   Function = what system does; Performance = how system performs [OK]

Hint: Capacity = functional; speed = non-functional [OK]

Common Mistakes:

• Classifying capacity as non-functional
• Mixing performance with system capabilities
• Ignoring the difference between function and quality