concept
Architectural Driver
The small subset of requirements and constraints that actually shape the structure of the system.
Most requirements do not affect architecture. A driver is one that does: if it changed, the structure would have to change too.
Drivers come in four kinds — the handful of functional requirements that are structurally significant, the quality attributes with hard targets, the technical and organisational constraints that cannot be negotiated, and the explicit architecture principles the organisation has already adopted.
Identifying drivers is the first real act of architecture, because it is what makes the design tractable. A system may have 400 requirements and six drivers. Design against the six.