Functional and Non-Functional Requirements

There is a huge difference between a functional and a nonfunctional requirement. The functional requirement describes the tasks that a software must do, while the nonfunctional requirement describes how the software will do.

The functional requirements most of the time describe the behavior of the function, such as instructions or tasks regarding something. In software, these requirements describe the way it functions.

The following functional requirements are some of the most common:

  • Business Rules
  • Transaction corrections, adjustments and cancellations
  • Administrative functions
  • Authentication
  • Authorization levels
  • Audit Tracking
  • External Interfaces
  • Certification Requirements
  • Reporting Requirements
  • Historical Data
  • Legal or Regulatory Requirements

The nonfunctional requirements are re remaining requirements of a project, in the case of software, they describe the what the software is going to do or how. These requirements specify in general the product, rather than an specific task or method.

The following nonfunctional requirements are some of the most common:

  • Performance – for example Response Time, Throughput, Utilization, Static Volumetric
  • Scalability
  • Capacity
  • Availability
  • Reliability
  • Recoverability
  • Maintainability
  • Serviceability
  • Security
  • Regulatory
  • Manageability
  • Environmental
  • Data Integrity
  • Usability
  • Interoperability

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