Functional vs non-functional requirements in Software Engineering - Hands-On Comparison

Understanding Functional vs Non-Functional Requirements

📖 Scenario: You are part of a software development team planning a new mobile app for a local library. To make sure the app meets users' needs, you need to clearly list what the app should do and how well it should perform.

🎯 Goal: Build a clear list that separates functional requirements (what the app must do) from non-functional requirements (how the app should behave or perform).

📋 What You'll Learn

Create a dictionary called functional_requirements with exactly these entries: 'User login': 'Allow users to log in with email and password', 'Search books': 'Enable searching books by title, author, or ISBN', 'Borrow books': 'Allow users to borrow available books'

Create a dictionary called non_functional_requirements with exactly these entries: 'Performance': 'App should load pages within 2 seconds', 'Security': 'User data must be encrypted', 'Usability': 'App must be easy to navigate for all ages'

Create a list called all_requirements that combines the keys from both dictionaries in this order: functional requirements first, then non-functional requirements

Add a final statement as a string variable called summary that explains the difference between functional and non-functional requirements in one clear sentence

💡 Why This Matters

🌍 Real World

Software teams use functional and non-functional requirements to plan and build software that meets user needs and quality standards.

💼 Career

Understanding these requirements is essential for roles like business analysts, project managers, and software developers to ensure successful software delivery.

1

Create functional requirements dictionary

Create a dictionary called functional_requirements with these exact entries: 'User login': 'Allow users to log in with email and password', 'Search books': 'Enable searching books by title, author, or ISBN', and 'Borrow books': 'Allow users to borrow available books'.

Software Engineering

# Create the functional_requirements dictionary with the specified entries
# Your code here

Hint

Use curly braces {} to create a dictionary with the exact keys and values given.

2

Create non-functional requirements dictionary

Create a dictionary called non_functional_requirements with these exact entries: 'Performance': 'App should load pages within 2 seconds', 'Security': 'User data must be encrypted', and 'Usability': 'App must be easy to navigate for all ages'.

Software Engineering

functional_requirements = {
    'User login': 'Allow users to log in with email and password',
    'Search books': 'Enable searching books by title, author, or ISBN',
    'Borrow books': 'Allow users to borrow available books'
}
# Create the non_functional_requirements dictionary with the specified entries
# Your code here

Hint

Use a dictionary just like in Step 1, but with the new keys and values.

3

Combine requirement keys into a list

Create a list called all_requirements that contains all keys from functional_requirements first, followed by all keys from non_functional_requirements, preserving their order.

Software Engineering

functional_requirements = {
    'User login': 'Allow users to log in with email and password',
    'Search books': 'Enable searching books by title, author, or ISBN',
    'Borrow books': 'Allow users to borrow available books'
}

non_functional_requirements = {
    'Performance': 'App should load pages within 2 seconds',
    'Security': 'User data must be encrypted',
    'Usability': 'App must be easy to navigate for all ages'
}
# Create the all_requirements list combining keys from both dictionaries
# Your code here

Hint

Use list() and .keys() to get keys from each dictionary, then add them together.

4

Add summary explaining the difference

Create a string variable called summary that explains the difference between functional and non-functional requirements in one clear sentence. For example, say that functional requirements describe what the system should do, while non-functional requirements describe how the system should perform or behave.

Software Engineering

functional_requirements = {
    'User login': 'Allow users to log in with email and password',
    'Search books': 'Enable searching books by title, author, or ISBN',
    'Borrow books': 'Allow users to borrow available books'
}

non_functional_requirements = {
    'Performance': 'App should load pages within 2 seconds',
    'Security': 'User data must be encrypted',
    'Usability': 'App must be easy to navigate for all ages'
}

all_requirements = list(functional_requirements.keys()) + list(non_functional_requirements.keys())
# Create the summary string explaining the difference between functional and non-functional requirements
# Your code here

Hint

Write a clear sentence as a string assigned to summary.

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