Functional and nonfunctional requirements are terms used in software engineering and systems engineering to describe different types of system or application specifications. Here’s an overview of each:
- Functional Requirements:
- Definition: These describe the behaviors, functions, and features that a system must possess. In essence, they answer the question “What must the system do?”
- Examples:
- A user must be able to log in using a username and password.
- The system should be able to generate and email monthly reports to users.
- A bank application should allow users to transfer money between accounts.
- Documentation: Often represented as use cases, user stories, or system functionalities in requirement documents.
- Nonfunctional Requirements:
- Definition: These describe the characteristics or attributes the system should possess, rather than specific behaviors. They often answer questions related to “How well must the system do something?” and can be related to performance, usability, reliability, etc.
- Examples:
- The application must have a response time of no more than 2 seconds under normal load.
- The system should be available 99.9% of the time.
- Data backups should occur nightly without any user intervention.
- The user interface should be intuitive and require minimal training for new users.
- Documentation: These requirements can be harder to quantify and measure, but they’re crucial for ensuring the quality, usability, and performance of the system. They can be captured in a system’s specifications, Quality of Service (QoS) metrics, or other specialized documentation.
It’s essential to note that both functional and nonfunctional requirements are crucial for the success of a project. While functional requirements outline the main functionalities the system should achieve, nonfunctional requirements ensure the system’s quality, performance, usability, and other critical factors. Properly defining and managing both sets of requirements can mean the difference between the success and failure of a software project.
