Functional Vs. Non-functional Requirements

---

---

Introduction to Requirements in Software Development

Functional Requirements

Define what the system should do. They define specific behaviours, features, and functionalities that the system must have to meet user needs. These requirements are usually expressed as actions or tasks the system should perform.

Examples

• User Authentication− The system must allow users to log in with a username and password.

• Data Processing− The system must process and validate user inputs in real-time.

• Reporting− The system must generate sales reports on a monthly basis.

Non-Functional Requirements

Define how the system should perform. They define the quality attributes, performance standards, and constraints that the system must adhere to. These requirements focus on aspects such as usability, reliability, security, and scalability.

Examples

• Performance− The system must handle up to 1000 concurrent users with response times of less than 2 seconds.

• Security− The system must ensure data encryption for all sensitive information.

• Usability− The system must be user-friendly and accessible to users with disabilities.

Types of Functional Requirements

• User Interface Requirements− Requirements related to UI components, layout, and design (e.g., a search bar).

• Business Requirements− Describe business rules and policies (e.g., the system should apply a tax rate based on location).

• Data Management Requirements− Define how the system should handle data input, storage, and processing.

• Administrative Requirements− Features for system administration, like user role management or access control.

Example Use Case

Describe a sample functional requirement and how it helps meet business objectives.

Types of Non-Functional Requirements

Performance Requirements

• Response times− the amount of time it takes for a system to react to a given input or request.

• Throughput− refers to the rate at which a system can process data or complete tasks within a given period of time.

• Latency− refers to the time delay between a user's action and the corresponding response from the system.

Examples

Response Time− The page should load in under 2 seconds for 93% of users.

Scalability Requirements

The systems ability to handle growth in data volume, users, or transactions.

Example− The system should support up to 10,000 concurrent users.

Security Requirements

Requirements for data protection, encryption, and access control.

Example− Passwords must be hashed and salted before storage.

Usability Requirements

Requirements related to the ease of use and learnability of the system.

Example− All core functions should be accessible with no more than three clicks.

Reliability and Availability Requirements

Defines the systems expected uptime and error tolerance.

Example− The system should have 99.9% uptime.

Maintainability and Portability

Requirements for the ease of maintenance, debugging, and migration.

Example− Code should follow documented standards to ensure maintainability.

Legal and Compliance Requirements

Regulations and standards the system must adhere to (e.g., GDPR General Data Protection Regulation)

Example− Users must consent to data usage in compliance with GDPR.

Techniques for Gathering Requirements

Interviews with stakeholders and users to capture expectations.

Surveys and Questionnaires for collecting feedback from a large audience.

Workshops and Brainstorming Sessions for collaborative requirement gathering.

Observation and Job Shadowing to understand real-world user interactions.

Document Analysis of existing systems and policies.

Prototyping and Mock-ups to visualize requirements and gather feedback.

Documenting Functional and Non-Functional Requirements

Requirements Documentation

• Software Requirements Specification (SRS) Documents− Used to capture both functional and non-functional requirements in detail.

• Agile User Stories and Acceptance Criteria− Defining "done" for each requirement.

Using Diagrams

• Use Case Diagrams− Visualizing functional requirements.

• Flowcharts and Sequence Diagrams− For process flows and system interactions.

Non-Functional Documentation

• Quality Attribute Scenarios− Describing non-functional requirements in scenarios (e.g., "In case of a server failure, the system should recover within 3 minutes").

• Best Practices− Ensuring requirements are clear, testable, and prioritized.

Challenges in Managing Functional and Non-Functional Requirements

• Ambiguity and Misinterpretation− Vague requirements lead to misunderstandings. Use clear, specific language. Changing Requirements: Requirements may change frequently; use Agile methodologies for flexibility.

• Conflict between Functional and Non-Functional Goals− Trade-offs may be required (e.g., security vs. usability).

• Prioritization Issues− High-priority non-functional requirements (like security) may be overlooked.

• Stakeholder Alignment− Ensuring all stakeholders agree on priorities and definitions.

Best Practices for Managing and Validating Requirements

• Involve Stakeholders− Regular stakeholder feedback ensures requirements align with expectations.

• Prioritize Requirements− Rank functional and non-functional requirements based on importance to the business.

Tests for Non-Functional Requirements

Load Testing for performance requirements.

Usability Testing for user experience.

Security Audits for security and compliance requirements.

Iterative Review and Refinement, Regularly revisit requirements for completeness and relevancy.

Use Automation, Track requirements in real-time, using tools like JIRA, Confluence, and Trello for traceability.

Summary

A balanced approach to functional and non-functional requirements is essential for building robust, user-centred software systems. This article highlights the definitions, types, and methods for gathering, documenting, and validating these requirements, ensuring software projects align with both user expectations and technical standards.