factors Requirements are generally described initially as non-functional requirements at the system level and system engineers must subsequently break down these system requirements very carefully as software or hardware requirements to comply with the human factor requirements of the system. Within the ECSS standards, numerous viewpoints and concepts are provided to describe various types of candidate human factors requirements at the system, software, and hardware levels. This document introduced a standards-based framework for specifying and measuring the software requirements for functions needed to meet system human factors requirements. The main contribution of this paper is our proposed generic software FUR model for system human factors requirements. This generic model can be considered as a kind of reference model for identifying the human factors requirements of the system and can be used for their assignment to the software functions that implement these requirements. The system requirements assigned to the hardware have not been addressed in this document. Since the generic model structure is based on the generic software model adopted by the COSMIC measurement standard, the information needed to measure their functional size is readily available and an example of a specific instance of this reference model has been presented. Specifically, the generic human factors requirements model presented in this document is based on: • The ECSS standards for describing the NFR for system human factors requirements; • The COSMIC measurement model of functional requirements. The proposed specification and measurement model is independent of the type of software and languages... middle of paper ......9759 [40] to achieve this level of detailed inputs of human factors requirements earlier in the cycle life of the project (i.e., at the end of the software requirements phase, rather than much later, in the software testing phase. The proposed human factors requirements reference model presents a way to measure these FURs with COSMIC – ISO 19761, to take this into account in FSM-based software estimation models, thus avoiding late discovery of mandatory FURs leading to budget overruns and missed deadlines. The measurement aspects presented in this paper have been limited to the system requirements assigned to the software. It will be interesting in future work to investigate whether or not this measurement approach can be extended to all these system-level requirements (i.e. all hardware-software-manual requirements, and not just software requirements).).