Is it acceptable to have the FRS as a stand along document without a URS document?

[CQAO_GEN]

Dear Aron,
as my point of you is not a best practice. but i do agree it's done in common practice. URS is intended to capture around a business process all regulatory and criticla business needs to perform their business without focus on "a specific system" where the FS comes with a system solution to address some of those needs whereas other URS will be address by process or manual mitigation controls. if we mix both there is a risk to omit some requirements from process view and to focus on operating software capabilities.

[RPR Consulting]

The short answer is yes, it is acceptable to have separate documents. However, this is where the use of a Traceability Matrix may be useful. In my experience, the FRS is often (usually) a separate document from the URS, but they should, as you state, be in lockstep. A Traceability Matrix describes the links between all the various components within the requirements documents, ideally from specification through to (successful) testing.

[WillC]

I'm not sure there is any mandate to have both URS and FRS, though in a complex system it may make sense to separate them. The decision should be part of an objective risk-proportionate approach - would it make any difference to the overall quality/safety of the system? Inspectors don't like to see corners being cut, but if you can justify your approach you should be fine.