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Broadly, functional requirements define what a system is supposed to do and non-functional requirements define how a system is supposed to be.Functional requirements are usually in the form of "system shall do <requirement>", an individual action or part of the system, perhaps explicitly in the sense of a mathematical function, a black box description input, output, process and control ...
Functional requirements are supported by non-functional requirements (also known as "quality requirements"), which impose constraints on the design or implementation (such as performance requirements, security, or reliability). Generally, functional requirements are expressed in the form "system must do <requirement>," while non-functional ...
Within systems engineering, quality attributes are realized non-functional requirements used to evaluate the performance of a system. These are sometimes named architecture characteristics, or "ilities" after the suffix many of the words share. They are usually architecturally significant requirements that require architects' attention. [1]
A software requirements specification (SRS) is a description of a software system to be developed.It is modeled after the business requirements specification.The software requirements specification lays out functional and non-functional requirements, and it may include a set of use cases that describe user interactions that the software must provide to the user for perfect interaction.
FURPS is an acronym representing a model for classifying software quality attributes (functional and non-functional requirements): Functionality - Capability (Size & Generality of Feature Set), Reusability (Compatibility, Interoperability, Portability), Security (Safety & Exploitability)
A functional requirement in a functional specification might state as follows: When the user clicks the OK button, the dialog is closed and the focus is returned to the main window in the state it was in before this dialog was displayed. Such a requirement describes an interaction between an external agent (the user) and the software system ...
When talking about architecture, the terms non-functional requirements or quality attributes are often used. [2] However recent empirical studies show that, for a software system, not all non-functional requirements affect its architecture, and functional requirements can also affect its architecture.
Within the application boundary, non-functional requirements are associated with relevant categories and their sub-categories. Using a standardized set of basic criteria, each of the sub-categories is then sized according to its type and complexity; the size of such a requirement is the sum of the sizes of its sub-categories.