Glossary · Engineering, integration and validation
Functional specification
Also known as: FS, Functional design specification
German: Funktionsspezifikation
In automation and software engineering, a functional specification describes what a system must do to meet the user requirements: its functions, operating modes, interfaces, alarms and performance, from the user's and process view rather than as a technical design.
- Validation
In one sentence
A functional specification describes what a system must do to meet user requirements: functions, modes, interfaces, alarms and performance.
Example
The functional specification of the batching system defines the recipe phases, the allowed operator interventions and the alarm response for each phase.
How it applies
- Engineering: The functional specification answers the User requirements specification (URS) and is refined by the Design specification. Each Functional requirement should be testable.
- Testing: In a V-model, the functional specification is verified by system tests, often during the Factory acceptance test (FAT).
- Regulated industries: In GAMP-style Computerized system validation (CSV) and computer software assurance (CSA), the functional specification is a controlled deliverable traced to requirements and tests.
- Documentation: The documentation team uses the functional specification to plan user documentation, but writes instructions from the as-built system and checks every function described there against the final software.
Functional specification vs. design specification
The functional specification describes the system's behavior; the Design specification describes the technical solution that realizes it. Keeping them separate makes it possible to change the design without reopening agreed functions.