## 2 Research Background
### Understanding of the Digital Twin
#### 2.2.2 Application along the Asset Life Cycle  
The concept of DTs is designed to accompany the entire product lifecycle of an asset and, depending on the respective phase, to provide corresponding services and benefits. In general, a DT focuses on the design, development, operation and decommissioning phases of assets [41]. DTs can be used to develop new products more responsively, better informed, and more efficiently. In addition to improved data feedback, early use in development provides a basis for collaboration between development and production and enables the synergetic integration of knowledge gained from production or operations into product development, which can lead to significant improvements in the quality of a product. With regard to production, DTs are considered capable of monitoring and controlling complex production processes in real time and optimizing the processes through timely adjustments [29]. Along the life cycle, DTs also promise benefits in operations and maintenance [15]. For example, researchers recommend the use of DTs in the aviation industry, where DTs are implemented to replace conventionally used methods of real-time monitoring to accurately predict relevant events. By integrating historic, fleet and sensor data and combining it with intelligent services, the prediction of aircraft life and fleet maintenance can be improved and facilitated [17]. However, these benefits in the operation and maintenance of an asset are not limited to the aerospace industry [18]. In additive manufacturing, for example, DTs are used to predict the cooling rate, temperature gradient, micro-hardness, velocity distribution and solidification parameter with increased accuracy to enable improved operation and predictive maintenance [17,18]. In addition to the use of DTs in industry, there are also use cases in the logistics sector, which have, however, been little researched to date. In logistics, the described ability of real-time monitoring enables real-time communication between products and different systems [16]. Based on the collected data sources, realistic performance indicators can be determined in real time, which contribute to targeted decision-making. DTs, thus, offer considerable potential in logistics [27]. In addition, DTs also provide added value for the operating resources used in logistics systems along their respective life cycles. Furthermore, DTs will play a central role in the realization of holistic asset management of critical rail transport components, as they build the basis for a CDE of the rail industry [36]. Regarding the life cycle of assets described before, the concept of DTs is of great importance. Due to the possible mapping of only a potentially real system or asset, i.e., a prototypical artefact, a distinction is made in DTs between _digital twin prototypes_ (DTP) and  
Figure 1: Specific DT concept in the context of DB; source: own illustration based on [12,27,30,32,33]. digital twin instances_ (DTI) [42] (see Figure 2). The DTP is a DT that contains information records necessary to describe or create a physical system. These information records can range from simple parts lists to fully annotated 3D models. DTIs, on the other hand, are DTs that describe a specific real physical system. They can but not must represent the further development of a DTP and can vary arbitrarily in their characteristics regarding the information data sets [41]. Both DTPs and DTIs are operated and used in their environment, the DTE [9; 42]. An example of a so-called DTP in rail transport could be a virtual prototype of a high-speed train such as the German _Intercity-Express_ (ICE) 4, which could be used for operationally optimal research and development. The DTP is crucial here because it allows product developers to realize enormous cost and time savings while avoiding the consumption of resources and potentially dangerous situations [29]. Furthermore, DTIs can be designed to carry out simulations and derive recommendations for action or even make automated decisions [31].