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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 ...
When discussing 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 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]
Generally, functional requirements are expressed in the form "system must do <requirement>," while non-functional requirements take the form "system shall be <requirement>." [3] The plan for implementing functional requirements is detailed in the system design, whereas non-functional requirements are detailed in the system architecture. [4] [5]
FURPS is an acronym representing a model for classifying software quality attributes (functional and non-functional requirements): Functionality - capability (size and generality of feature set), reusability (compatibility, interoperability, portability), security (safety and exploitability)
Architectural decisions influence and impact the non-functional characteristics of a system. Each architectural decision describes a concrete, architecturally significant design issue (a.k.a. design problem, decision required) for which several potential solutions (a.k.a. options, alternatives) exist.
For example, a non-functional requirement to be free from backdoors may be satisfied by replacing it with a process requirement to use pair programming. Other non-functional requirements will trace to other system components and be verified at that level. For example, system reliability is often verified by analysis at the system level.
The ARCADIA method applies to the design of complex and critical systems, and more generally architectures that are subject to multiple functional and non-functional constraints, including software, electronic, electrical architectures, and industrial processes. It defines a set of practices that guides needs analysis and design to meet an ...