Flow-down consists of writing requi

Flow-down consists of writing requirements for the lower level elements in response
to the allocation.

When a system requirement is allocated to a subsystem, the subsystem must have at least one requirement that responds to the allocation.


The lower-level requirements either may closely resemble to the higher level or may be very different if the system engineers recognize a capability that the lower level element must have to meet the higher-level requirements.

The lower-level requirements are often referred to as derived requirements [14]. Derived requirements are requirements that must be imposed on the subsystem(s). These requirements are derived from the systems decomposition process.

There are two subclasses of derived requirement, i.e. subsystem requirements and interface requirement.

The subsystem requirements are the requirements that must be imposed on the subsystems themselves but do not necessarily provide a direct benefit to the end user.

Interface requirements are the requirement that arise when the subsystems need to communicate with one another to accomplish an overall result.
This result is needed to share data or power or a useful computing algorithm.