Be it systems engineering or software engineering, functional requirements define what a product shall do like the action to be performed to satisfy the fundamental reason for its existence. It is with these functional requirements that a business analyst/requirements engineer explains to the developers the expectation of a product for further development.

To explain the requirements better to the developers the business analyst/requirements engineer may make use of Business Use case (BUC) scenarios. When the stakeholders reach consensus the business analyst/requirements engineer specifies the functionality indicated by a given scenario to be used by the developers.

What is a functional requirement?

Functional requirements are meant to capture the intended behaviour of a system. Functional requirements can be expressed as tasks, services or functions that the system shall perform and can vary based on the context under which it is being created. Functional requirements can be calculations and technical details, data processing, processing and other specific functions that define what the system is supposed to achieve. While capturing the functional requirements one may make use of use cases. Under the ambit of requirements engineering use cases are created post elicitation of requirements and validation. So if one takes into account the hierarchy of functional requirements then one can drill down this way:
·Stakeholder need
·Identification of feature
·Creating use cases
·Finalising business rule

The process of creating a functional requirement

A functional requirement shall contain a unique number, name to be identified & referenced in addition to a brief summary and a rationale behind. Through this arrangement an intended reader shall have necessary information to understand a requirement better and track it through the entirety of a system development. The mentioned requirement stated must be clear and readable. All these requirements that are being described come from:
·The rules required for the business
·From the organisation (or)
·Through the interaction from the various stakeholders, sponsors or Subject Matter Experts (SME) present within an organisation.

Some examples of functional requirements