Non-functional requirement
A non-functional requirement describes a solution’s quality or constraints. It can be as mandatory as a functional requirement.
A non-functional requirement describes a solution's quality attributes or constraints. These can include response times or technical restrictions. “Non-functional” means neither unimportant nor optional.
A hypothetical search project requires 95% of searches to display complete results within at most 2 seconds with 1000 items and 10 simultaneous test users. Measurement runs from submitting the search to the complete display in the agreed test environment. These are example targets, not measured ASES values or performance promises.
“Search is fast” would be too vague for this. Alongside a limit, there must be an understandable measurement method and suitable conditions. Classification as a quality requirement says nothing about priority: it can also be a must-have requirement.
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Related terms
- Requirements catalogueA requirements catalogue organises requirements with identifiers and verifiable details. It helps track scope, unresolved questions and changes.
- Must-have requirementA must-have requirement is essential to the agreed delivery scope. Without it, the intended outcome is not acceptable within that scope.
- Service level indicator (SLI)An SLI is a clearly defined measure of an aspect of service quality that matters to users.
- Exit strategyA prepared route to switch, take over or retire an IT service in an orderly way.
- Migration costsEffort and expenditure for the planned move of data or functions to another environment.
- Investment costsCosts of building a new or expanded IT capability, as considered in project planning.
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