## 2 Theoretical Fundamentals and State of the Art
Taking a globalized and interconnected supply chain approach into account, the role of standardized interfaces is therefore crucial for further superordinate supply chain optimization. To make use of new technologies and support the premises of Industry 4.0, individualization, flexibility, decentralization, and resource efficiency, various technologies have to be combined. When operating within the production site scale, this digitalization development within such a facility are combined and defined as Smart Factory [36; 37; 38; 39; 40]. According to [40], a Smart Factory can be described as a compound of Cyber-Physical Systems (CPS) connected by the Internet of Things (IoT), to support humans and machines in their activities [34]. As stated by [2; 35; 41; 42; 43; 44], key technologies, especially for the metal forming industry, include a generic infrastructure, consisting of CPPSs, IIoT, DTs, Big Data, and Cloud Computing. Considering the already existing infrastructure within the heavy industry segment focused in this work, the integration of already existing technology by using a brownfield approach results in a mixed form of this theoretical construct: expensive layer 0-4 solutions already implemented but not fulfilling these new requirements cannot be exchanged without unreasonable investments. This statement is especially important for SMEs, which tend to have a generally lower budget for innovation that usually amortize in a medium to long-term period. To be able to unite already existing structures with these Industry 4.0 (I 4.0) related technologies, a generic infrastructure, serving as a standard for internal and external technological communication must be implemented. To create a uniform understanding of I 4.0 technologies and their standards, the RAMI 4.0 framework, based on the Smart Grid Architecture Model (SGAM) [2; 45; 46; 47], was developed. RAMI 4.0 can therefore be understood as a structured approach to I 4.0 in order to enable uniform communication between its users. The most important interrelations between key aspects of I 4.0 are visualized by three axes. For the success of a digitalized process chain, there must be a holistic, corresponding vertical and horizontal integration along the life cycle and value stream. As shown in Figure 1, the \"Life Cycle and Value Stream\" represents the life cycle of physical entities, including the product, along the process chain over which the horizontal and vertical integration takes place [2; 45; 46]. Horizontal integration, represented by the hierarchy levels ensures cross-border communication with other entities, representing one of the fundamental premises of I 4.0 [2; 45; 46]. Vertical integration takes place across the layers and is used for data integration and communication between those [2; 45; 46]. The RAMI 4.0 model consists of the following layers (Figure 1):  
* The Asset layer describes the lowest layer in RAMI 4.0 and contains all physical objects;* The Integration layer is representative for the connection of physical objects with the digital domain and contains the required hardware and software;
* The Communication layer executes the digital connection and thus can be seen as an IIot equivalent;
* The Information layer contains all process-relevant data and information in different formats;
* The Functional layer contains all functions of a value chain. Depending on their determination, these functions can be of a logistical or data processing character;
* The Business layer houses the business logic and deals with the optimization of products and processes. The hierarchy level is distinguished as follows (Figure 1):  
* Product describes the product to be manufactured;
* Field Device includes entities for collecting data, such as sensors and data acquisition (DAQ);
* Control Device describes those operating elements that are used to control the system;
* Station describes the machine or station used for the production step;
* Work Center is to be understood as the production environment;
* Enterprise describes the host enterprise itself.