## 2 Research Background
### Development of Systems  
To secure problem-oriented DT development, the needs of people and organizations involved must be recognized and integrated, as it is with systems [17; 25; 42]. A _system_ represents the purposeful sum of its components, which are used in an organized way to achieve specific functions. Hereby, the interaction and combination of the individual components as well as the interaction with its environment are crucial [21]. Regarding the development of systems containing software, a categorical distinction is made between technically computer-based and socio-technical systems. _Technically computer-based systems_ consist of hardware and software components that do not contain processes and persons for the purpose-free fulfilment of functions [25]. _Socio-technical systems_ contain one or more technical systems and, in addition, to define work processes, are characterized by the fact that there are dedicated persons who understand, monitor, and understand the system. Thus, these are systems with interactions between social and technical systems, so-called human-machine interactions. The work processes and responsible operators within the system are clearly defined [43]. The core of a socio-technical system is the technical system with the work processes. Socio-technical systems are mostly business systems that are designed to support the fulfilment of business objectives. Thus, the company's policies, cultural values, strategies, and goals, as well as national laws and regulations, influence the procurement, development and use of the system. In this context, the system boundaries can be variable, as there are different views in science on the extent of the integration of corporate layers [25]. Figure 2: Interoperability of DTs along the asset lifecycle. In the context of this work, the layered structure of socio-technical systems and DTs is understood to include all these levels. An example of socio-technical systems is a railway control system of railway undertakings, as it includes, in addition to the many hardware and software components of the technical system, indexed persons such as dispatchers who make decisions on the basis of the computer system [44]. Thus, it can be concluded that the corporate environment in which socio-technical systems are used has a decisive influence on the development process of the systems [25]. The term of _systems-engineering_ (SE) is the basis for the development of such systems and defines its development processes. Due to the high system complexity, SE encompasses a multitude of activities consisting of specification, development, validation, deployment as well as operation and maintenance of the system [25; 45]. These are developed considering the hardware and software characteristics as well as the human factor. Socio-technical systems can be classically divided into seven layers. Table 1 illustrates the close interlocking of the SE within the different layers and reveals a holistic approach, since--contrary to classical software engineering--micro- and macro-economic as well as hardware-technical aspects are covered. Thus, the focus lies on the whole system and enables the inclusion of a wide range of system-specific factors, which makes the SE a suitable starting point for the successful GIS development [25]. Every system, whether it is real or virtual, has a life cycle. In the classical sense, a life cycle model represents the abstract and functional description of the conceptualization, realization, use, further development and decommissioning of a system. A system evolves because of actions. These actions are carried out and controlled with the use processes by those responsible for the system [21; 25; 46]. The SE described is supplemented by the IEEE 15288 standard (2015), which contains all processes of the SE and serves the successful realization of a system. The standard focusses on the early integration of stakeholder needs and required system functionalities to secure a problem-oriented solution development and validation.