Software Engineering
Functional and Non-Functional Requirements in Software Engineering
Introduction
Requirements engineering is a critical phase in software development that establishes the foundation for successful software systems. Understanding the distinction between functional and non-functional requirements is essential for creating comprehensive and effective requirements specifications. This section explores these two fundamental types of requirements and their importance in the software development process.
Functional Requirements
Functional requirements define the specific behaviors and functions that a software system must perform. They describe what the system should do from the user’s perspective and typically include:
Types of Functional Requirements
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Functional Specifications: Detailed descriptions of specific features and functions
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User Stories: Concise descriptions of functionality from the user’s viewpoint
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Use Cases: Scenarios that illustrate how users interact with the system
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Business Rules: Regulations that govern system behavior
Examples of Functional Requirements
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The system shall allow users to reset their passwords
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The application must display search results within 2 seconds
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Users can filter products by price range and category
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The software shall generate monthly reports in PDF format
Non-Functional Requirements
Non-functional requirements define the quality characteristics and constraints of a software system. They specify how the system should perform its functions and include:
Types of Non-Functional Requirements
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Performance Requirements: Response times, throughput, and resource utilization
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Security Requirements: Authentication, authorization, and data protection
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Usability Requirements: User interface design and accessibility
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Reliability Requirements: System availability and fault tolerance
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Scalability Requirements: Ability to handle increased loads
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Maintainability Requirements: Ease of modification and updates
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Compatibility Requirements: Integration with other systems and platforms
Examples of Non-Functional Requirements
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The system shall handle at least 10,000 concurrent users
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All user data shall be encrypted both at rest and in transit
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The application shall be accessible to users with visual impairments
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The system shall recover from hardware failures within 5 minutes
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Response time for critical operations shall not exceed 1 second
Requirements Engineering Process
1. Elicitation
Gathering requirements through interviews, workshops, and observations with stakeholders.
2. Analysis
Organizing and prioritizing requirements while resolving conflicts.
3. Specification
Documenting requirements in a clear, unambiguous format.
4. Validation
Verifying that requirements are correct and complete through reviews and prototypes.
5. Management
Tracking requirements changes and ensuring traceability throughout development.
Techniques for Gathering Requirements
User Interviews
Conducting one-on-one discussions to understand user needs.
Focus Groups
Facilitating group discussions with multiple stakeholders.
Surveys and Questionnaires
Collecting feedback from large user groups efficiently.
Observation
Watching users interact with existing systems to identify pain points.
Document Analysis
Reviewing existing documentation to identify requirements.
Requirements Documentation
Software Requirements Specification (SRS)
A formal document that describes the system’s intended functionality and constraints.
Requirements Traceability Matrix (RTM)
A tool for tracking requirements throughout the development lifecycle.
Validation and Verification
Verification
Ensuring requirements are complete, consistent, and feasible.
Validation
Confirming that the developed system meets the documented requirements.
Common Challenges in Requirements Engineering
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Ambiguous or conflicting requirements
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Changing requirements during development
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Overlooking non-functional requirements
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Inadequate stakeholder involvement
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Unrealistic expectations
Best Practices
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Involve stakeholders throughout the process
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Prioritize requirements based on business value
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Use prototypes to clarify requirements
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Maintain requirements traceability
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Regularly review and update requirements documentation
Conclusion
Understanding and properly documenting both functional and non-functional requirements is essential for developing software systems that meet user needs while maintaining quality, performance, and security. By following systematic requirements engineering processes and best practices, development teams can create comprehensive requirements specifications that guide successful software development.
This concludes Section 4.1, “Functional and Non-Functional Requirements,” of the Software Engineering course. If you want to read the previous chapter, check out 3.8 Software Configuration Management. For the complete syllabus, visit Syllabus Link. Continue your learning with the next chapter: 4.2 Requirements Engineering Process.