# Function-Oriented Applicability Evaluation of Technical Folding Based on Expert Knowledge
## 1 Introduction
### Problem Identification and Research Need  
The following chapter discusses which data from early phases of the function-oriented product development process can be considered as a knowledge database for the software-supported applicability evaluation. It also defines the research questions arising from the use of these data as a basis for software-supported evaluation of a solution principle.  
In function-oriented product development processes, requirements, functions, and function structures of a product are available as a knowledge database for evaluating the applicability of solution principles [23; 24; 25]. Requirements are regulatory restrictions in product development, quantifiable limitations of the product, or describe the desired product behaviour [23; 24]. Requirements can be formalised using standardised, syntactic sentence structure patterns [24]. As their formalisation is a challenge for a concise and software-supported evaluation due to the high variability of syntax and semantics, requirements should not be used as a database for software-supported applicability evaluation.  
Based on requirements, functions are derived during the product development process. Functions describe the desired product behaviour in a solution-neutral manner using the so-called subject-verb method and the definition of an incoming and outgoing function flow (e.g., \"reduce product size\", \"enlarge system\", or \"direct force\") [23; 24]. The overall function of a product describes its overall purpose and can be decomposed into subfunctions down to elementary functions. Elementary functions usually form the deepest level of the function structure and cannot be subdivided further. The meaningful linking of subfunctions and elementary functions to the overall function leads to the function structure [23; 24; 26]. Based on the functions, suitable principle solutions are sought using their physical effect [23; 24]. While functions describe the changes between incoming and outgoing function flows, physical effects concretise how this change is physically actualised [24]. Therefore, elementary functions and physical effects are linked to each other in order to work out a principle solution. As the assignment between elementary functions and physical effects of technical folding systems is not known so far, this assignment must be newly created. Alternatively, the assignment between functions (main or sub-functions) and solutions can also be derived backwards from the solution knowledge about existing technical folding systems [26]. Since technical folding systems are solutions in the sense of product development, the basic applicability of a solution can be identified on the basis of its functions. However, this raises the following main research question and subordinate research questions (1)-(3):  
How can the applicability of technical folding be assessed on the basis of function structures?  
1. What known technical folding solutions exist, and what do the associated function structures look like?
2. How can functions and function structures of published technical folding solutions be modelled in a formalised form as a _knowledge database_?
3. How can this _knowledge database_ be used in a software-supported method to assess the applicability of technical folding solutions to the current development task of a product developer?  
To answer these research questions, the EvalTech method based on case-based reasoning methods is designed in Section 3. Its central elements are developed in Section 4 and implemented in a MATLAB(r) application (The MathWorks Inc., MATLAB version: 9.13.0 (R2022b), Natick, MA, USA) in Section 5. The application is intra-operable with the systems engineering tool Cameo Systems Modeler(r) (Dassault Systemes, Cameo Systems Modeler version: 19.0, Velizy-Villacoublay, France).