# Function-Oriented Applicability Evaluation of Technical Folding Based on Expert Knowledge
## 4 Developing the Central Elements of the EvalTech Method
### Setting Up the Initial Database  
In order to create the initial _database_, functions of known, successfully implemented technical folding systems (cf. Section 2.2) are derived from the identified overall purpose and stored in a list. These functions are consolidated in a next step, and their duplicates removed. In this way, a total of 110 different functions could be identified. The functions identified include main functions, sub-functions, and elementary functions of technical folding systems. The main functions of technical folding systems are, for example, \"protect system\", \"transport system\" or \"replicate structure\". The main functions are divided into its sub-functions, such as \"reduce overall installation space\", \"establish connection\" or \"guide system\". Examples of identified elementary functions in folding systems are \"directing force\", \"collecting liquid\" or \"directing material\" clearly assigned to the elementary functions. These examples clearly show that main and sub-functions describe the specific product behaviour of technical folding systems, while elementary functions must be fulfilled in most mechanical and mechatronic systems and are therefore not specific to the technical folding solution principle. For this reason, elementary functions are not suitable for evaluating the applicability of the solution to the new technical problem and are deleted from the list. Subsequently, the frequency distribution of all functions remaining in the list was evaluated, and the ten most frequent functions were defined as _characteristic functions of technical folding_, cf. Figure 4. For example, the function \"reduce total installation space\" was identified in 17 out of a total of 21 technical folding systems, \"enlarge total installation space\" in 16 cases and \"establish connection\" in 14 cases. Functions that have been identified in more than 1/3 of the cases count as _characteristic functions_ in the context of this research paper.  
Figure 4: Frequency distribution of characteristic functions for technical folding systems with finite thickness.  
The naming of these functions has been worked out specifically for technical folding systems in the context of the DFG-funded project E\({}^{2}\)F, cf. Section 6.1.  
The _characteristic functions_ are stored as a part of _case base 1_ of the CBR system, cf. Section 3.1.  
_Case base 2_ of the general concept is created by forming the hierarchical function structures of 21 known technical folding systems on the basis of derived functions. The function structures are each stored in standardised adjacency matrices. Consequently, the _case base 2_ database consists of 21 cases. Folding-specific information about the technical folding system, such as the folding discipline, the folding scheme or the type of movement, cf. Section 2.2, are assigned as metadata to each _case_. Each _case_ thus corresponds to a function structure and metadata of a solution that has been successfully realised with technical folding.  
The following Figure 5 shows the hierarchical functional structure using the example of a self-deployable stent [7]. The model of each functional structure is created as a block definition diagram using the software Cameo Systems Modeler(r) (Dassault Systemes, France). For the formation and further use of the respective adjacency matrix, the block definition diagram is exported as a CSV file, and the adjacency matrix is derived.