Glossary · Requirements and interfaces
Constraint (systems engineering)
Also known as: Design constraint
German: Randbedingung
In systems engineering, a constraint is a limitation that restricts permissible design or operation, such as a standard, interface, environment or technology condition. It narrows the solution space rather than describing a function.
- Systems engineering
- Data and interfaces
In one sentence
A constraint limits permissible design or operation, from a mandated standard to a fixed interface, and must be traceable like any requirement.
Example
A retrofit project for a CNC machine has the constraint that the existing safety PLC and its fieldbus must be reused, which limits the choice of new drives and safety functions.
How it applies
- Requirements: Record constraints with a source and a rationale, like any requirement. An unexplained constraint is hard to challenge or remove later.
- Integrated systems: Existing interfaces, installed equipment and site conditions are common constraints in integration projects. They belong in the interface documentation as well.
- Machine safety: A constraint never justifies an unacceptable risk. If a constraint prevents adequate risk reduction, the constraint has to be revisited.
- Technical documentation: Operating constraints, such as ambient temperature or supply voltage, reappear in the instructions for use as conditions of intended use.
Constraint vs. assumption
A constraint is a limitation the design must respect. An assumption is a condition believed to be true but not controlled by the design. Assumptions need checking; constraints need compliance.