## 2 Research Background
### Understanding of the Digital Twin
#### 2.2.1 Definition of the Concept
GE Digital makes the connection to analytics tools and machine learning in terms of a DT's ability to run simulations, and sees the primary application areas in assets, networks and processes [38]. With reference to the maturity level of an implemented DT, Detecon addresses the level of communication between physical and virtual object as well as the degree of standardization of the data models and sources of a DT, whereby _standardization_ means the ability of the DT to exchange data with internal and external systems to be integrated into a multilateral ecosystem. According to this, a DT only exists if there is bi-directional communication between physical and virtual entities and interactions with one of the two entities have direct effects on the other and vice versa [39]. The environment in which the DT is to be implemented significantly influences the definition of a DT. In the context of this work, these external circumstances, also referred as the _digital twin environment_ (DTE), are mainly driven by the DB environment [9]. The IT subsidiary of DB defines DTs as a digital representation of objects, persons or processes that enable a comprehensive exchange of information and pursue the goal of optimizing a business result. Furthermore, they can contain \"algorithms, simulations and services that describe or influence past, present or future properties and behavior of the represented object\" [12]. To give justice to the scientific claim of this work, the definitions from science and practice are assembled with the philosophy of DB. Based on the described fact that no uniform DT definition exists, and that the definition is related to the case of application, this work is based on the following DT definition in the context of the research project:  
_\"The concept of the digital twin consists of a physical and virtual space in which four system platforms exist: the physical and virtual asset, the data management and the services. The different dimensions are interconnected and exchange data. The virtual system platform is a physically correct digital representation with very high fidelity of the physical system platform. The overall goal of a digital twin is to offer concrete services and business outcome in its environment. This serves the operational optimization of the asset under consideration along its life cycle.\"_  
This definition, which is illustrated in Figure 1, is kept general due to the objective nature of this work, and therefore, does not specify the maturity level of DTs in terms of communication and standardization, as well as the services and properties offered. Furthermore, it does not go into detail about the technologies that are necessary for the development and use of the DT, as these also depend on the specific use case. The term asset is chosen due to the fact that [40] is defines an object as an \"entity that has a perceived or actual value to an organization and is owned or managed individually by the organization\". The term thus covers the areas of DT application mentioned by DB Systel GmbH and is in line with science, as no clear definitions exist here.