# Testing a New Structured Tool for Supporting Requirements' Formulation and Decomposition
## 2 Materials and Methods  
### The Proposed Tool: A Structured Matrix for Requirements' Formulation  
As reported in Section 1, the proposed tool allows designers to consider the main functions of the products contextually and to allocate different requirements' categories to each function. The initial set of functions to be processed can be extracted by means of existing checklists. Indeed, the tool can implement any checklists among those available in engineering design literature and/or specifically proposed by engineering designers, e.g., for peculiar application fields [38]. However, as mentioned, the tool is thought of as particular support when integrated into systematic procedures for the design of physical products. Consequently, its validity in other contexts, e.g., information technology and/or software engineering, is not ensured. Moreover, the proposed tool allows its users to discern between wishes and demands. Indeed, although apparently similar, these two types of information are regarded as very different indications by designers [3]. The former are targets that guide the designer in the design space exploration but do not provide a specific value (e.g., \"maximize speed\", or \"minimize power consumption\"). Differently, demands provide precise values to be reached, e.g., \"the speed must be greater than 10 m/s\", or \"the power consumption must be lower than 20 kW\". As shown in Figure 1, the proposed tool appears as a matrix, which can be implemented in an electronic spreadsheet, thus allowing easy updates, sharing, and modifications. More precisely, each couple of rows represents a different entry from a reference checklist, further subdivided into design wishes and demands. This aims to make the tool extremely versatile, so that requirements' checklists using different types of triggers can be used alternatively or in a combined fashion. Differently, the groups of columns represent the main functions of the product. No specific concept of function is considered here, and the designer can use the most suitable one for their specific understanding, purpose and/or context. Accordingly, the definition of the main functions, i.e., what the product should do irrespective of specific solutions, is the very first step to be taken before the formulation of demands and wishes. After the identification of the main functions, the designer can formulate and then allocate each requirement by specifying:  
* Which kind of item is affected by the requirement (e.g., geometry, kinematic), by simply organizing the requirement into the desired couple of rows. * Whether the requirement is a wish or a demand, simply by putting the requirement in the desired row. * Which function is affected by the requirement, simply by locating it in the desired group of columns. It is important to recall that, as claimed in the Introduction, the proposed tool does not provide any support for the formulation of functions, but simply keeps track of those formulated by the designer. The structured matrix is in fact expected to support designers in formulating the design specification through the formulation of requirements, and/or the decomposition of initial needs into requirements, which is commonplace in (complex) systems engineering. In this respect, it is important to highlight that the proposed tool focuses on the fuzzy front end of the design process, differently from other approaches developed within the requirements' engineering discipline (e.g., [39; 40; 41]). Some of these approaches aim at providing structured tools to better manage the evolution of requirements along the  
Figure 1: Generalized version of the matrix (N checklist items and M functions). The number of columns under each function can vary. Empty boxes are allowed when it is not possible to extract/infer relevant requirements. different phases of the design process (e.g., [39]), or to model the decomposition in a function-based hierarchical fashion (e.g., [40]).