Functional Requirements in Software Development

Study Notes

Define the system's expected behaviour, tasks, or functions.
Describe what the system should do.
User-centric: derived from user or stakeholder needs.
Focus on the system's response to specific inputs or conditions.
Atomic and measurable: broken down into smaller, independent units.
Examples:
- User authentication: using username and password.
- Search functionality: by name, category or price.
- Report generation: financial reports at the end of each month.
- Inventory management: automatic stock level updates after sale.
Tools for documenting functional requirements:
- Use case diagrams: interactions between users and the system.
- User Stories: descriptions of features from the perspective of the end user (commonly used in Agile).
- Functional Specification Document (FSD): detailed document outlining all functional requirements.
Importance:
- Guide development: acts as a blueprint.
- Testing basis: create test cases to validate functionality.
- Stakeholder communication: align on what the system should do.
Challenges:
- Incomplete requirements: missing or vague requirements can lead to costly changes later.
- Changing requirements: impact project scope and timeline.

Specify criteria to judge a system's operation rather than specific behaviours.
Focus on system quality attributes rather than functionalities.
Describe how the system should perform.
Define system qualities: performance, security, scalability, maintainability, etc.
Global constraints: apply to the entire system.
Measurable metrics: defined using benchmarks.
Examples:
- Performance: respond to queries within 2 seconds.
- Security: all data must be encrypted using AES-256 encryption.
- Scalability: support up to 10,000 concurrent users.
- Availability: 99.99% uptime (excluding scheduled maintenance).
- Usability: accessible to visually impaired users (WCAG 2.1 standards).

Performance:
- Response time, throughput, resource utilisation.
- Example: handle 500 transactions per second.
Security:
- Data protection, authentication, authorisation.
- Example: Only authorised users can access the administrative dashboard.
Reliability:
- Function correctly under specific conditions.
- Example: operate continuously for 24 hours without failure.
Usability:
- Ease of use, user-friendliness.
- Example: new users should be able to navigate the system with minimal training.
Scalability:
- Ability to manage increased demand.
- Example: support 10,000 additional users without a performance drop.