## 2 Requirements in Design Processes: Open Issues, Relevance and Implications  
The Special Issue received 12 submissions, out of which 7 contributions passed the review process and have been published. The topics mainly refer to methodological approaches dealing with the analysis, assessment, and management of requirements and applications to case studies in several fields. In the following, a summary of the published papers is provided. In [1], an approach based on living systems is presented, which is dedicated to the identification of gaps and potential improvements in the formulation of requirements. More specifically, the method provides support for product reengineering tasks that are specifically oriented towards the achievement of disruptive innovations. Beyond the description of the methodological approach, the paper presents an application to an illustrative case belonging to the cybersecurity field. Contribution [2] presents a user-centered methodology to support product design, which primarily considers requirements in functional and aesthetic perspectives. The designer's role and responsibility are also taken into account. A case study shows how the proposed methodology can support the designer in selecting among design alternatives and in reducing potential biases and subjective decisions. Contribution [3] describes a method for the systematic assessment of requirement change risks, which has been developed by using a multiple case-study approach. More specifically, the change risk was assessed by combining change likelihood and change impact, while propagation effects are considered by analyzing requirement interrelations. Furthermore, a software prototype was developed to enable the technology transfer to industrial applications. The study described in [4] revisits some assumptions of the conventional prescriptive and descriptive models of design. Furthermore, it investigates whether conventional models can also be applied for representing problem-solution co-evolution patterns that appear during conceptual design activities and that affect requirements consequently. The findings demonstrate co-evolution patterns that cannot be described by the conventional models as well as some inconsistencies. In [5], a new formulation of the design requirements in Natural Laminar Flow (NLF) optimization tasks is presented to make them less experience-based and much more grounded on quantitative criteria. The paper shows the impact of the proposed formulation on the result of NLF optimization in the design of transonic airfoils and aero-enginecompressor blades from two perspectives: Pareto front convergence and the improving effect of accessory performance. Contribution [6] deals with the lack of structured processes to extract relevant information for benchmarking purposes in Product Planning. It presents an approach to identify and structure the relevant knowledge for innovating a product radically with respect to the definition of requirements. The proposed method is applied to the sector of agricultural machines, which is characterized by a high degree of maturity and, predominantly, incremental innovations. Eventually, in [7], a structured tool was presented, which is capable of allocating different requirements to specific functions systematically and to discern between design wishes and demands. The tool can be integrated with different requirement checklists to enhance their performance in extracting useful information for product developments. Moreover, an experiment as described to assess the efficacy of the proposed approach. Overall, the approaches presented in the accepted papers illustrate a variety of alternatives for handling requirements and how the alternatives considerably affect the design process as a whole. The contributions show how fields of application, designers' culture, and preferred methodologies play roles in requirement processing. A holistic and comprehensive model of design requirements' management and transformation during design phases is far from being developed.