## 2 State-of-the-Art
### Platform Ecosystems  
In recent years, platforms have arisen in many business fields in order to bring together customers and providers and offer innovative services. In this respect, the term platform is used very frequently; however, its meaning is not clear and consistent [37]. In the scientific literature, three perspectives on platforms from the fields of engineering, economics, and organization can be found [38]. Considering this, platforms offer a medium of interaction for business partners based on software, hardware, organizational processes, and standards [39]. Platforms are characterized by a layered architecture [40] and act as a central cornerstone, which supplies core functionalities [41]. In this way, they offer a common access point for users and a set of basic services [42]. Ecosystems and platforms are closely connected with each other because ecosystems are platforms in which numerous firms can contribute components (e.g., apps) to a technical platform [43]. Hence, the term \"platform ecosystems\" is also frequently used [44; 45].  
From an economic perspective, platform ecosystems offer several major benefits, especially the co-creation of business value by encouraging complementary invention and exploiting network effects, as well as increasing flexibility [42]. The fact that five out of the ten most valuable brands are built on platform business models demonstrates these outstanding advantages [46]. Regarding platform ecosystems, there are several aspects to consider. Platforms may result in a winner-takes-all situation, where eventually, the free competition of different vendors is eliminated and substituted by a single dominator [47]. However, there are also systems aiming at co-evolution promoting symbiotic situations, which provide benefits for all participants. In this way, the complementors, which contribute, e.g., applications to the platforms are crucial, because they moderate the competition [48]. Therefore, platform users should be able to easily exchange services from different vendors and, in doing so, avoid so-called vendor lock-in. Another characteristic of platform ecosystems is the indirect network effects, where the value of a product increases with the total number of users [42], e.g., platforms with a high number of potential customers are very attractive for vendors. Consequently, the thresholds and obstacles for participants need to be minimized, in order to make it easy for new partners to participate in an ecosystem. This effect was for example studied by [49], where the pricing of gaming hardware, which indicates the entry hurdles for a video game console, was proven to be crucial for the success of vendors. Moreover, platform ecosystems benefit highly from complementary inventions from other partners and thereby value co-creation, as by this means, new and innovative services can be offered [50].  
To coordinate the variety of platform participants, a suitable governance approach is also required. The governance of a platform ecosystem is of contingent and dynamic nature and has to be carried out by the platform operator [51]. Thereby, standardization is an important element for governance. Moreover, due to the situational and temporal contingencies, establishing self-selection is very effective [52]. This means the participants self-select the different partner levels and define the appropriate rules for their business.  
Overall, platform ecosystems play a very important role in the business world and bring some major advantages. Nevertheless, establishing and running a platform ecosystem includes some challenges. Platform ecosystems are already widespread in the manufacturing sector and energy markets; the existing solutions are outlined below.