# Towards Integrated Digital Twins for Industrial Products: Case Study on an Overhead Crane
## 4 Discussion
### Hypotheses Review  
We now review the eight hypotheses shown in Section 1.1. The review is based on the experiences of one environment during a relatively short time, and should therefore be taken as indicative rather than conclusive. **Hypothesis 1**. : _Digital twin transforms data from a physical product to useful knowledge. Digital twin offers data and knowledge to all stakeholders across the product lifecycle._  
The bearing lifetime estimation and brake condition monitoring case focus strongly on turning data to knowledge through multi-phase data processing. The usage roughness indicator also turns raw data into more sophisticated information about how the crane is being handled. The design automation case uses existing knowledge of the application and turns data into an actionable solution. The web UI shows data rather than transforming it into knowledge. Hence, turning data into knowledge seems to be crucial in some cases, but not in all. This emphasizes that digital twins are defined by their use case, and different features of DTs have different purposes. The Ilmatar DT as a whole provides the data or knowledge to designers, maintainers, and users of the crane, although each case focuses on just one stakeholder. Currently, these cases are fragmented, and serving all stakeholders from one digital twin demands a lot of integration. Both of the claims of hypothesis 1 can be fulfilled if the digital twin is a combination of multiple cases and they are often perceived as goals for twins, but they are not general requirements for digital twins. **Hypothesis 2**. : _Digital twin integrates digital models and data from different sources and providers and offers a customized view for each stakeholder._  
The models and data used for the components of the design and maintenance focused DT cases come mainly from the manufacturer and the crane itself. The operator focused applications heavily rely on crane data, but also leverage external data, such as the additional sensors of the high precision lifting case and the environment data of the LIDAR-based pathfinding case. Hence, it seems that design and maintenance can rely on data from a limited amount of sources, whereas operation focused applications also crave other data sources. Although, it may also be that we did not find the right supplementary data for design and maintenance purposes. Integrating the work to a single digital twin proved to be more difficult than expected, but is still seen as a prominent development direction. The existence of customized views is initially verified, as the components of Ilmatar digital twin offer views for machine design and maintenance as well as operators. In addition, sales have been identified as another relevant stakeholder. Each of these groups needs a customized view to achieve their goals. **Hypothesis 3**. : _Digital twin enables networking and business._  
Networking has several points of validation across the use cases, although they come with two preconditions: functional interfaces and a commonly beneficial use case. The digital twin concept itself as well as the buzzwordiness of the term acted as business networking enablers. Actual business creation is more difficult to validate in the context of this externally funded research project as most of these were made as proof-of-concept prototypes instead of business-critical applications. The usage roughness case had clear API-based boundaries of responsibility between the two organizations, which enabled efficient information exchange. The clear boundaries can be thought of as a networking enabler thanks to the efficiency of communication they offer, and we find it probable that if taken to a business context, the API-based responsibility boundaries will enable easier business creation. The bearing use case combined most parties to one case: one company provided a use case, the university acted as an integrator and application builder, a second company provided analysis algorithms and the end application was integrated to the PLM software upkept by a third company.