Understanding Common Functional and Non-Functional Requirements in Software Engineering

Developing software solutions requires gathering and defining various types of requirements These requirements act as a blueprint that outlines what the system should do and how it should perform As a software engineer or project manager, having a solid understanding of the common functional and non-functional requirements is key to delivering successful projects that meet stakeholder needs.

In this comprehensive guide, we will explore what functional and non-functional requirements are, provide common examples, and discuss best practices for gathering and documenting these requirements.

What are Functional Requirements?

Functional requirements define the core capabilities and behaviors that a system needs to fulfill its intended purpose. In simple terms, functional requirements describe what the software system should do.

Some common types of functional requirements include:

• User requirements – These describe the features and functionalities required by end-users to achieve their goals For example, user login, search functions, reporting features etc

• Business requirements – These specify the business processes and rules that need to be supported by the system. Such as order management, payment processing, compliance with regulations etc.

• System requirements – These outline technical behaviors and functions required for the software to work such as interface requirements, calculations, workflows etc.

• Integration requirements – Requirements related to integrating the system with external applications, data sources or services

Properly gathering and documenting functional requirements is crucial as they define the scope of the software to be built. Some best practices include:

• Involving key stakeholders early through interviews and workshops.

• Using user stories, use cases, user scenarios to detail requirements from an end-user perspective.

• Creating mockups and prototypes to better visualize and validate requirements.

• Writing functional requirements clearly using simple language.

• Structuring requirements using a standard template for consistency.

• Prioritizing requirements based on business value and dependencies.

• Reviewing requirements with stakeholders frequently for feedback.

• Maintaining traceability between requirements and other technical artifacts.

What are Non-Functional Requirements?

While functional requirements define the intended behavior and functions, non-functional requirements specify the quality attributes and performance standards that the system should meet. In other words, non-functional requirements focus on how the system should work.

Some of the most common non-functional requirements include:

• Performance – Such as response time, latency, throughput, capacity etc.

• Scalability – Ability of the system to handle increased load.

• Reliability – The level of stability and availability of the system.

• Security – Data security, access control, and measures to prevent unauthorized access.

• Usability – The ease of use of UI and navigation for end users.

• Maintainability – Ability to make changes and add new features easily.

• Portability – Ability of the system to work on different platforms and devices.

• Compatibility – How well the system integrates with specific technologies, browsers etc.

Documenting non-functional requirements well is important to set appropriate expectations on quality of service and user experience. Some tips include:

• Gathering specific metrics and benchmarks from stakeholders.

• Prioritizing vital NFRs like security, performance, reliability early.

• Creating measurable and testable non-functional requirements.

• Considering non-functional needs across the entire system lifecycle.

• Reviewing NFRs continuously and updating as needed.

• Tracking non-functional requirements separately from functional ones.

Real-World Examples of Common Functional and Non-Functional Requirements

Let’s look at some real-world examples of common functional and non-functional requirements for various types of software systems:

Example 1: Online Retail Website

• Functional

  • User accounts – sign up, login, profile management
  • Product catalog browsing and faceted search
  • Shopping cart and order management
  • Payment processing and transactions
  • Order tracking system
  • Inventory management and stock updates

• Non-Functional

  • Website performance – fast page load times
  • Reliable service with 99.95% uptime
  • Ability to handle traffic surges during peak events
  • Secure handling and storage of customer data
  • Mobile responsiveness and multi-device compatibility
  • Intuitive and user-friendly interface

Example 2: Accounting Software

• Functional

  • User and access management
  • General ledger, accounts receivable/payable
  • Invoicing, billing and payment processing
  • Financial and cash flow reporting
  • Fixed assets and depreciation management
  • Payroll management
  • Taxes and compliance management

• Non-Functional

  • Accuracy of financial calculations
  • Data integrity and auditability
  • System interoperability with banking applications
  • Role-based access controls and permissions
  • Scalability to handle multiple countries/entities
  • Availability of 24×7 technical support
  • Easy upgrades and migrations

Example 3: Real-Time Communications Platform

• Functional

  • Presence management
  • Instant messaging, voice and video calling
  • Screen sharing collaboration
  • File sharing and transfers
  • Conference calling and virtual meetings
  • Call management features – mute, hold, transfer etc.
  • Chatbot integrations

• Non-Functional

  • Media quality and low latency for real-time apps
  • Cross-platform support across devices
  • Reliability of 99.99% uptime
  • Peak concurrency capacity of 50,000 users
  • End-to-end encryption for secure communications
  • Easy deployment through containers/Kubernetes
  • Localization and multi-language support

Best Practices for Managing Requirements

Proper requirements management is key to prevent issues like cost/schedule overruns, poor product quality, and stakeholder dissatisfaction. Here are some best practices:

• Prioritization – Classify requirements based on priority – high, medium, low. Focus on highest priority ones first.

• Traceability – Maintain associations between requirements and other artifacts like design documents and test cases.

• Version Control – Manage changes to requirements systematically using version control tools like Git.

• Validation – Confirm requirements by prototyping or getting sign-offs from stakeholders.

• Communication – Document requirements clearly and communicate frequently with team members and stakeholders.

• Agile Methods – Gather requirements iteratively using user stories and product backlogs rather than big upfront.

• Change Management – Record and analyze impact of requirement changes through change control processes.

• Tools – Use specialized requirements management tools for enhanced traceability and reporting.

Key Takeaways

• Functional requirements define the capabilities and features of a software system. Non-functional requirements specify quality attributes and performance standards.

• Some common functional requirements are user, business, system and integration requirements. Common non-functional requirements include performance, security, reliability, and usability.

• Best practices for requirements include iterative elicitation, clear documentation, validation, prioritization, traceability and change control.

• Examples of requirements vary across different types of software – retail, accounting, communications etc. Requirements should be tailored to project context.

• Managing requirements systematically is essential for delivering projects successfully and keeping stakeholders satisfied.