Nonfunctional requirement

As explained in Functional Design and Architecture: Examples in Haskell

A nonfunctional requirement specifies general qualities or operational constraints of an application rather than specific functions.

A nonfunctional requirement specifies the general properties and operational constraints an application must satisfy, rather than the functions it performs. In a spacecraft system, robustness, fault tolerance, continuous operation, ease of use, security, compatibility, performance, stability, extensibility, availability, capacity, and latency are nonfunctional requirements. section 1.2.1

Spacecraft control software

Manual and automatic control are functional requirements because they describe what the software does. Operating reliably around the clock, remaining secure, processing the required amount of data, and avoiding a rewrite as the system evolves are nonfunctional requirements that shape its design. section 1.2.1

Figure 1.4 Compromising between simplicity, goals, and requirements

Use the trade-off diagram to relate simplicity, goals, and requirements when choosing a design that remains maintainable. section 1.2.1

How Functional Design and Architecture: Examples in Haskell covers it

How deep it goes

Defines the category and distinguishes it from functional requirements through spacecraft properties and maintainability concerns.

Examples

Uses spacecraft reliability, fault tolerance, continuous operation, security, compatibility, capacity, and latency as examples.

What it assumes

Assumes understanding of applications and user tasks while introducing the distinction between functional and nonfunctional requirements.

What you can do after

Evaluate design goals by separating required behavior from qualities that constrain implementation and future maintenance.

How it connects

Connects functional requirements with performance, stability, extensibility, availability, security, latency, and maintainability.

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Also explained in

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  Delivering Machine Learning Projects: From design to deploymentA nonfunctional property describes an operational characteristic of data, such as its scale, speed, history, or update frequency.
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  Software Design for Python ProgrammersA nonfunctional requirement is a requirement specifying a quality, constraint, or condition on how an application operates rather than a specific capability.
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  Object-Oriented Software Design in C++A requirement that imposes a constraint on an application's qualities, operation, environment, or implementation-independent behavior rather than specifying a discrete feature.
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  Kafka for ArchitectsA non-functional requirement specifies a quality attribute, constraint, or operational characteristic of a system rather than a business function.
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  Machine Learning System DesignA requirement that specifies qualities or operational constraints of a system, such as performance, security, or portability.

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Related concepts

• requirementskind of · A requirement is a stated need, capability, quality, condition, or constraint that a system, product, solution, or project is expected to satisfy.
• functional requirementcontrasts with · A functional requirement specifies a behavior or capability that a system must provide or enable.
• scalabilityincludes · Scalability is the ability of a system, process, or method to accommodate increasing workload, size, or demand while maintaining acceptable operation.
• performanceincludes · Performance is the measurable effectiveness or operational behavior of a system under specified conditions, assessed through relevant qualities such as task results, speed, responsiveness, throughput, or resource use.

This explainer was generated by Manning's knowledge graph from the text of Functional Design and Architecture: Examples in Haskell. The section links point to the parts of the book it draws on.