Functional vs. Non Functional Requirements

Requirements analysis is an essential process that enables the success of a system or software project to be assessed. Requirements are generally split into two types: Functional and Non-functional requirements. functional requirements define the specific behavior or functions of a system. In contrast, non-functional requirements specify how the system performs its tasks, focusing on attributes like performance, security, scalability, and usability.

What are Functional Requirements?

These are the requirements that the end user specifically demands as basic facilities that the system should offer. All these functionalities need to be necessarily incorporated into the system as a part of the contract.

• These are represented or stated in the form of input to be given to the system, the operation performed and the output expected.
• They are the requirements stated by the user which one can see directly in the final product, unlike the non-functional requirements.

Examples:

• What are the features that we need to design for this system?
• What are the edge cases we need to consider, if any, in our design?

What are Non-Functional Requirements?

These are the quality constraints that the system must satisfy according to the project contract. The priority or extent to which these factors are implemented varies from one project to another. They are also called non-behavioral requirements. They deal with issues like:

• Portability
• Security
• Maintainability
• Reliability
• Scalability
• Performance
• Reusability
• Flexibility

Examples:

• Each request should be processed with the minimum latency?
• System should be highly available.

What are Extended Requirements?

These are basically "nice to have" requirements that might be out of the scope of the System.

Example:

• Our system should record metrices and analytics.
• Service heath and performance monitoring.

Examples of Functional and Non-functional Requirements

Let's consider a couple of examples to illustrate both types of requirements:

1. Online Banking System

1. Functional Requirements:

• Users should be able to log in with their username and password.
• Users should be able to check their account balance.
• Users should receive notifications after making a transaction.

2. Non-functional Requirements:

• The system should respond to user actions in less than 2 seconds.
• All transactions must be encrypted and comply with industry security standards.
• The system should be able to handle 100 million users with minimal downtime.

2. Food Delivery App

1. Functional Requirements

• Users can browse the menu and place an order.
• Users can make payments and track their orders in real time.

2. Non-functional Requirements:

• The app should load the restaurant menu in under 1 second.
• The system should support up to 50,000 concurrent orders during peak hours.
• The app should be easy to use for first-time users, with an intuitive interface.

Differences between Functional Requirements and Non-Functional Requirements:

Below are the differences between Functional Requirements and Non-Functional Requirements:

Importance of Balancing Both Functional and Non-Functional Requirements

As functional and non-functional requirements address distinct but equally significant components of the system, it is essential that they be balanced in system design. Here's why balancing them is essential:

• Improves User Experience: A system that functions but is slow, unresponsive, or challenging to operate could be the consequence of concentrating only on the functional requirements. Usability, performance, and availability are examples of non-functional criteria that have a big influence on how users interact with the system and how satisfied they are.
• Enhances System Performance: Scalability, dependability, and security are examples of non-functional features that guarantee the system operates effectively in real-world situations. Failure may ensue from a system that satisfies functional requirements but is unable to scale or manage a high user volume. By keeping these in balance, the system is guaranteed to function properly.
• Prevents Bottlenecks and Failures: Systems that function well but lack security or dependability are more likely to experience malfunctions, breaches, or outages. The system is made more robust and less vulnerable to bottlenecks by taking non-functional criteria into account.
• Reduces Long-Term Costs: Systems designed with only functional requirements in mind often encounter scalability and maintainability issues as they grow. Addressing non-functional requirements early on prevents costly changes, re-architecting, or performance enhancements later.
• Supports System Evolution: Non-functional requirements such as maintainability and extensibility make future updates, feature additions, and system scaling easier and less disruptive. This balance ensures that the system can evolve and adapt over time without significant hurdles.

Common Challenges in Defining these Requirements

Defining both functional and non-functional requirements in system design can be challenging due to several factors. Here are some common challenges:

• Ambiguity in Requirements: Requirements are often unclear, making it difficult to interpret what the system should do (functional) and how it should perform (non-functional).
• Changing Requirements: As projects evolve, functional and non-functional requirements often change due to shifting business goals, market trends, or user needs.
• Difficulty in Prioritization: Deciding which functional and non-functional requirements are most important is often difficult. Functional needs can overshadow non-functional ones, such as security or scalability.
• Measuring Non-Functional Requirements: Functional requirements are often straightforward to test, but non-functional requirements like usability, scalability, and reliability are harder to measure and validate.
• Overlapping or Conflicting Requirements: Sometimes, functional and non-functional requirements can overlap or conflict. For example, adding complex security features (non-functional) might slow down the performance (another non-functional requirement).

How to Gather Functional and Non-functional Requirements

Gathering requirements involves multiple approaches and collaboration between the development team, stakeholders, and end-users:

1. Functional Requirements:

• Interviews: Talk to stakeholders or users to understand their needs.
• Surveys: Distribute questionnaires to gather input from a larger audience.
• Workshops: Host sessions to brainstorm features and gather feedback.

2. Non-functional Requirements:

• Performance Benchmarks: Consult with IT teams to set expectations for performance and load.
• Security Standards: Consult with security experts to define the best practices for data protection.
• Usability Testing: Test the system to find areas where users might struggle and refine the interface.