A comparative experiment between textual requirements and model-based requirements on proxies for contractual safety

Requirements form the backbone of contracting in acquisition programs. Requirements define the problem boundaries within which contractors try to find acceptable solutions (design systems). At the same time, requirements are the criteria by which a customer measures the extent that their contract has been fulfilled by the supplier. In this context, the quality of a requirement set is determined by the level of contractual safety that it yields. Unfortunately, textual requirements do not provide acceptable levels of contractual safety, as they remain a major source of problems in acquisition programs. Model-based requirements have been proposed as an alternative to textual requirements, although this promise has not been demonstrated yet. This paper addresses the main question of whether using model-based requirements improves the contractual safety of acquisition programs compared to using textual requirements. The level of adequate applicability, bounding, necessity, and completeness achieved by model-based requirements are empirically measured using an experimental study with aerospace engineering and industrial and systems engineering students on a space system application. The results show that model-based requirements outperform textual requirements in these four variables.