Towards the formalization of non-functional requirements in conceptual design

This paper explores the formal roles of non-functional requirements' (NFR) elicitation, definition, and verification in the early stages of an engineering design project. This is performed using a case study conducted at an automotive original equipment manufacturer (OEM) during the design and development of a rear bumper sub-system. The purpose of this exploration is to determine if NFRs should be formalized within requirements modeling scheme. This can capture conceptual design information to identify their impact on other requirements while conducting design changes. The modeling scheme in this paper consists of a sequence of following domains-requirements, functions, working principle, components, design parameters, test measures, and tests-that are mapped to each other using matrices. It is revealed through this case study that non-functional requirements drive much of the design decision-making process and constrain the manner in which the product functionality is realized. Hence, the inclusion of NFRs as a separate and distinct domain in the design process is critical to recognize their significance during design changes. Based on the observations made in the case study, the NFR domain is included in the requirements modeling scheme.