When designing a software system, it’s essential to identify and document the requirements that will guide the development process. These requirements can be broadly categorized into two types: functional and non-functional requirements. In this tutorial, we’ll explore the differences between these two types of requirements, provide examples, and discuss their importance in software design.
Functional Requirements
Functional requirements describe what a software system should do. They specify the functions or behaviors that the system must perform to meet the needs of its users. These requirements are often documented as use cases, which illustrate the interactions between the user and the system. Examples of functional requirements include:
- A system must send an email whenever a certain condition is met (e.g., an order is placed, a customer signs up, etc.)
- A payroll system must generate electronic fund transfers, calculate commission amounts, calculate payroll taxes, and report tax deductions to the IRS
- An e-commerce website must allow users to browse products, add items to their cart, apply offers and deals, and successfully place orders
Functional requirements are typically detailed and specified in the system design. They describe the specific behaviors or functions that the system must perform to meet the needs of its users.
Non-Functional Requirements
Non-functional requirements, on the other hand, place constraints on how the system will perform its functions. They specify criteria that can be used to judge the operation of a system, such as performance, security, usability, and reliability. Examples of non-functional requirements include:
- Emails should be sent with a latency of no greater than 12 hours from the triggering event
- The system must be available 24/7 with no downtime
- The system must respond to user input within 2 seconds
- The system must be able to handle a minimum of 100 concurrent users
Non-functional requirements can be divided into two main categories: execution qualities and evolution qualities. Execution qualities are observable at runtime, such as security and usability, while evolution qualities are embodied in the static structure of the software system, such as testability, maintainability, extensibility, and scalability.
Importance of Requirements
Both functional and non-functional requirements are essential in software design. Functional requirements ensure that the system meets the needs of its users, while non-functional requirements ensure that the system performs its functions efficiently, securely, and reliably. By identifying and documenting these requirements, developers can create a system that meets the needs of its users and is maintainable, scalable, and reliable.
Best Practices
When working with functional and non-functional requirements, it’s essential to follow best practices such as:
- Documenting requirements clearly and concisely
- Prioritizing requirements based on user needs and business goals
- Ensuring that requirements are testable and measurable
- Involving stakeholders in the requirement gathering process
- Reviewing and updating requirements regularly
By following these best practices, developers can create a software system that meets the needs of its users and is efficient, secure, and reliable.
Conclusion
In conclusion, understanding functional and non-functional requirements is crucial in software design. By identifying and documenting these requirements, developers can create a system that meets the needs of its users and is maintainable, scalable, and reliable. Remember to follow best practices such as documenting requirements clearly, prioritizing requirements, and involving stakeholders in the requirement gathering process.