## 2 State-of-the-Art
### Platform Ecosystems
#### 2.5.1 Manufacturing IT Platforms  
Modern manufacturing systems require multiple IT systems, which operate on different operational levels, to make the complex and numerous processes controllable. A commonly-used reference model to structure these manifold software solutions in a functional and hierarchical manner of five levels is the automation pyramid [53]. As every level may consist of several individual elements, shaping a suitable architecture to achieve an integrated information flow and meet all functional requirements is challenging. In line with the increasing digitization, cyber-physical systems, which merge the physical and virtual world through embedded hardware and software, present a new approach [54; 55; 56]. Thus, the conventional pyramid architecture is supplemented or replaced by a decentralized and non-hierarchical structure with increasing agility and flexibility [57]. Nevertheless, an architecture following the automation pyramid is still common in present-day manufacturing system architectures, which may also be indicated by its adaption within the Reference Architectural Model Industry 4.0 [58]. In order to handle increasing complexity and in line with the trend of digitization, manufacturing IT platforms, which cover all levels of the automation pyramid, are commonly applied. In addition, customers and suppliers are able to interact on these platforms, shaping complex ecosystems [59]. Driven by the recent trend towards increasing service orientation, also referred to as XaaS [60], many authors [61; 62; 63; 64] and companies have begun to work on service-oriented and often cloud-based platform ecosystems. They focus on the efficient provision of functionality in the form of software services for end users and are, therefore, well suited for applications in manufacturing. Compared to consumer-grade software platforms, industrial-grade manufacturing IT platforms have additional requirements [65; 66]. Reliability and security are central. While reliability ensures that the platform is capable of supporting 24/7 manufacturing, information and data security are necessary to protect the intellectual property of the company. Manufacturing IT platforms are offered by leading equipment and software vendors such as Predix by General Electric ([[https://www.ge.com/digital/iiot-platform](https://www.ge.com/digital/iiot-platform)]([https://www.ge.com/digital/iiot-platform](https://www.ge.com/digital/iiot-platform))), MindSphere by Siemens ([[https://siemens.mindsphere.io](https://siemens.mindsphere.io)]([https://siemens.mindsphere.io](https://siemens.mindsphere.io))), IoT Suite by Bosch ([[https://www.bosch-iot-suite.com](https://www.bosch-iot-suite.com)]([https://www.bosch-iot-suite.com](https://www.bosch-iot-suite.com))), and Avoom by Trumpf ([[https://marketplace.axoom.com](https://marketplace.axoom.com)]([https://marketplace.axoom.com](https://marketplace.axoom.com))), as well as by new developments in research such as the Industrial Data Space ([[https://www.internationaldataspaces.org](https://www.internationaldataspaces.org)]([https://www.internationaldataspaces.org](https://www.internationaldataspaces.org))) or Virtual Fort Knox ([[https://virtualsoftknox.de](https://virtualsoftknox.de)]([https://virtualsoftknox.de](https://virtualsoftknox.de))). These platforms aim at supporting manufacturing companies in networking their manufacturing and generate added value through digital services such as process optimization or predictive maintenance. Most existing and commercially available manufacturing IT platforms are tailored to products and services offered by the respective vendor [65; 66]. They utilize proprietary interfaces and protocols instead of open ones. As a consequence, neither interaction with external systems nor interoperability with other platform vendors are possible. This causes vendor lock-in effects for the customer, which is one of the largest barriers that companies face when introducing cloud platforms [67; 68].