# Towards Integrated Digital Twins for Industrial Products: Case Study on an Overhead Crane
## 4 Discussion
### Managerial Implications  
The most important takeaway from the development of digital twin applications for Ilmatar crane was the significance of easy-to-use APIs. They seem currently undervalued and leveraging them properly would offer significant efficiency boosters. Crucial  
Figure 14: Flowchart for acquiring API resources for a digital twin (DT) application development project as observed during the example project. The diamonds are fairly quick checks, whereas the rectangles represent various amounts of work. (e.g., building a reusable API requires more work than building a case-specific API.) Hence, rectangles should be avoided to get started with actual application development as fast as possible. Notes: The word “workers” refers to all the project workers collectively, i.e., it is enough that one of the workers has a specific skill. As an alternative for workers learning new skills, the project can also use outside support to perform the consequent tasks, although this may lead to a prolonged dependence of the support and possibly including the support in updating the use case requirements. Defining and updating the use case requirements is included in the chart as they proved to be inseparably dependent on the availability of suitable APIs. factors for achieving integrated digital twins include also a purposeful use case and cross-organizational leadership. In the long run, the role of open standards and open-source software need to be acknowledged and developed intentionally. Easy-to-use APIs are important because they are a requirement both for building integrated digital twins and for browsing digital twin data. Ease of use is of course a subjective matter, varying per person, and it is important specifically as such. The APIs need to be usable for those who need the data in their work; it does not help if they are usable for the most experienced developer in the company. Unfortunately, current methods to view the data from APIs are often cumbersome. For example, the user interface of the popular API browser \"Postman\" (PostMan, Inc., San Francisco, CA, USA, [[https://www.postman.com/](https://www.postman.com/)]([https://www.postman.com/](https://www.postman.com/))) relies heavily on typing text instead of offering clickable buttons. This text-based UI may be preferred by developers thanks to its versatility, but it is impractical for someone with little programming experience who just wants to browse the data behind the API. Contrastingly, the OPC UA client \"UaExpert\" (Unified Automation Gmbh, Kalchreuth, Germany, [[https://www.unified-automation.com/products/development-tools/uaexpert.html](https://www.unified-automation.com/products/development-tools/uaexpert.html)]([https://www.unified-automation.com/products/development-tools/uaexpert.html](https://www.unified-automation.com/products/development-tools/uaexpert.html))) has a graphical interface that allows browsing by clicking through a tree-like structure. MindSphere offers a graphical web user interface for browsing the historical data. We recommend decision-makers to demand this kind of usability from all API providers (both internal and external). To test usability, you can simply ask yourself: Can you browse the data behind the API? If not, probably neither can the majority of your employees, which makes developers a constant bottleneck for data access throughout the organization. APIs offer a whole new view to operations and enable innovations, but only if they are accessible. We recommend treating APIs as investments. A purposeful use case is a starting point for the actual digital twin development. The digital twin development for the Ilmatar crane started out by defining a common use case, which led to the formation of the bearing lifetime estimation case that had roles for all but one of the project partners. Other cases were defined among fewer participants and led to isolated twin applications. Combining these all to one twin proved both technically difficult and lacked purpose.