## 5 Discussion
### Relevance for Science and Practice  
#### 5.2.1 Limitation and Need for Further Research  
The GIS presented is used for the implementation of DTs, which represent assets in operation within logistics systems of German rail transport. Thus, the application is limited to assets that have already been developed and therefore physically exist. In the context of German rail transport and DB, for example, this means an operating signal box or an operating ICE train. Consequently, regarding Section 2.3, the GIS is limited to the implementation of DTs and DTs for existing assets. Thus, future research could focus on the development of a GIS for DTs used in the development of assets in production. The potential of doing so is also confirmed in the other papers [17]. In addition, the aforementioned work by [PERSON] et al. provides a detailed overview of existing theories and research on the topic of DT use for product development [18]. Despite the necessary consideration of the described aspects, the research has shown that the implementation of a DT is elementary for the perspective interoperable exchange with other (sub-) systems. The work of [PERSON] et al. confirms that and outlines further that to ensure interoperability between the DTs, several standardization issues, such as the synchronization of the physical asset and its DT, syntax and semantic interoperability needs to be addressed [54]. It has become clear that further research and development of standards is required and that this can only be conducted in dialogue with stakeholders and the industry. This dialogue is also of essential importance regarding the acquisition of data. Therefore, it could be concluded that in the considered use case, it is necessary to enter negotiating and contractual processes with the manufacturer at an early stage to obtain access to the relevant status data through a software update. However, due to the research framework, this was not explored in further detail and represents a starting point for further research work (see Sections 4.1 and 5.1). In addition to the establishment of these standards and data property, there is also a need for organizational research and development at DB, as regulatory framework conditions prevent the free exchange of data between subsidiaries of DB. With a view to the technological results, it has also been shown that the use of individual technologies is shaped by and depends on the use case. Nevertheless, the use of cloud services, also with a view to interoperability, is to be considered elementary. Based on the results analysis, it was also possible to develop functional and non-functional requirements as well as a reference architecture for the DT of an ICE asset. In particular, the requirements obtained represent new findings for science and practice, as no suitable references could be found. These must be further researched and developed in the future. Looking into the application of the GIS, it has been shown that the data collected during the research validates the solution approach. Still, the focus was on the first three technical processes of the GIS (see Figure 7). The processes four to fifteen as well as the supporting processes were not an active target component of the implementation and validation. Based on the results, it could be concluded that the interaction of technical and supporting processes during the implementation of DTs is essential, because as mentioned, such as the restriction of data acquisition and the contractual dialogue with manufacturers to be aimed for, are essential for the future implementation of DTs. Their application and investigation in further research, are therefore, recommended. This could lead to new insights into implementation inhibiting and facilitating factors that support the further establishment of DTs. With a view to practice, potentials were identified in which DT is promising in solving operational challenges.