## 3 Development of the Generic Implementation Strategy
### Methodological Fundaments of the Development
#### 3.1.1 Structure and Rationale of the Approach
Regarding the aspect of whether categories need to be added, it could be stated that the study by [17] is one of the few studies with a generic approach and the only study with a complete socio-technical system focus. It is also almost the only study to include the implementation environment and stakeholders in the process of developing a DT. In this study, this process is very closely aligned with the life cycle phases of the concept of DTs (i.e., design, development, operation, and decommissioning). Since this is in line with the stages of SE as well as the life cycle of systems mentioned in Section 2, another category, _orientation along the life cycle phases of a digital twin, was_ introduced. However, it is also apparent  
Figure 3: Methodical procedure concept of this work; source: own representation based on [30,48]. from this study that, despite an orientation that makes sense for answering the research questions of this work, there is a lack of details on how the described implementation strategy of DTs can be implemented [17]. For this reason, a category named _sufficient level of detail of the approach_ was introduced as well. The upper categories _functional_ and _non-functional_ proved to be useful due to the orientation of this work, as functional and non-functional requirements are also spoken of in classical SE. For this reason, they were retained as central superordinate categories. Through the content delimitation of the categories, four sub-upper categories were established, which are _functionalities_, _use case_, _procedure_, and _SE_. Figure 4: Qualitative content analysis of relevant DT research papers. The coding and evaluation of the research papers has shown that [PERSON] et al. investigate the process of implementing a DT for the management of complex satellite production processes. In doing so, [PERSON] et al. recommend a DT reference model and illustrate its implementation [49]. [PERSON] et al. develop a framework for implementing DTs in the use case of the product life cycle of production lines. They address the interaction of the real and virtual space as well as the connecting layer of information processing. They functionally structure these into data storage, processing and mapping, which forms the core of their DT framework [28]. [PERSON] et al. recommend a generic approach to modelling DTs in the context of a case study on predictive maintenance of industrial robots [50]. [PERSON] et al. focus on providing a DT approach for optimization and quality control within product assembly. In doing so, they recommend an implementation strategy for developing a platform that will serve as the basis for a subsequent DT application [51]. [PERSON] and [PERSON] develop a DT system architecture for the practical implementation of a DT prototype in surface-oriented assembly. Hereby, the architecture consists of three functional layers: operation, visualization and information layers [52]. [PERSON] et al. focus on developing a framework for implementing DTs that meets the requirements of synchronous operation of production and logistics. In doing so, [PERSON] et al. aim at merging the services of DTs and product service systems, which focus on the manufacturing phase [53]. [PERSON] et al. describe current technologies related to DT and recommend a reference model of a DT for process plants, which should serve the safety and risk management of its operators. In doing so, [PERSON] et al. divide the reference model into four layers: industrial process layer, communication system, DT, and user layer. In their work, it should also be emphasized that the reference model developed does not have a socio-technical system focus, despite the explicit focus on the interaction between people and machines [54]. [PERSON] et al. investigate the development of DTs in the context of manufacturing considering the socio-technical system focus for the first time and therefore clearly differentiate themselves.