# Structuring Reference Architectures for the Industrial Internet of Things
## 5 Considered Reference Architectures
### International Data Space (IDS)  
The IDS focuses on secure and trustworthy data exchange patterns in the manufacturing domain. The IDS Reference Architecture Model [25] (IDS-RAM) consists of five layers to establish interoperability and three crosscutting perspectives for reaching its main target, namely to ensure end-to-end data sovereignty of the data owner. The syntactic interoperability is accomplished by the IDS Connectors with their standardized interfaces and exchange protocols.  
The Viewpoints of the IIRA map only to a limited extent to the IDS Layer model. The scope of the IDS leads to a stronger focus on configuration, modeling and integration aspects mainly regarded from a system integration point of view. The IIRA scope includes more stakeholders resulting in several 'Viewpoints'. In general, the aspects of IDS Reference Architecture are mentioned in the IIRA's Functional Viewpoint. The layers and perspectives of the IDS-RAM can--to some extent--be mapped to the IIRA domains of the mentioned Functional Viewpoint.  
RAMI4.0 outlines a comprehensive view of manufacturing related aspects in an IoT landscape. Its focus is on the Asset and its digital representation, the Administration Shell, as its first class citizen. In contrast to that, IDS focuses on the data and data exchange while RAMI4.0 mainly specifies the integration of shop floor and office related components. Each architecture therefore targets different challenges of industrial IoT. This observation is also presented in Figure 6 where the purple colored concerns depict the issues of physical objects and the description of data entities. Concerns of security, authentication but also deployment of digital components (mainly found in the blue-colored intersection) are less covered. One can also notify that interoperability-related concerns (green) are relevant for the RAMI4.0, the IIRA and the IDS Reference Architecture Model. In addition, RAMI4.0 has a stronger view on physical objects (part of purple) and IDS-RAM on data and usage control (part of brown).  
Obvious similarities are the Business and Functional Layers in both reference models. Disregarding the same terminology, IDS and RAMI interpret the meaning differently. In the context of RAMI4.0, the Business Layer contains organizational and economic aspects as monetary conditions and legal regulations. On the other hand, IDS-RAM considers business related aspects, as for example, the role of a participant in the data exchange network.  
The Functional Layer in terms of the IDS comprises its core functional requirements and considerations, mainly data sovereignty, trustworthy interactions and supported data exchange. In contrast, RAMI defines its Functional Layer as a view regarding and describing abstract capabilities and _functions_ of assets and data workflows.  
Network and integration related topics as defined by the RAMI Layers Communication and Integration are combined in the IDS System Layer. The different focus of the IDS considers a suitable communication level through internet standards as a precondition. RAMI, targeting also non-IP-capable devices, defines fine-grained views on connection patterns but also on representing and identifying real-world objects as digital entities. The Asset Layer further strengthens the viewpoint by defining and providing the physical entity. In contrast, a physical object is only regarded by its digital representation in the context of the IDS.  
The major differences between both models is the emphasis on the cross cutting perspectives (IDS) and life cycle and hierarchy dimensions (RAMI). In order to enable a cross-organizational data exchange, security, certification and governance are the key consideration at all levels for the IDS. RAMI's focus on the integration of physical objects and manufacturing plants take these aspects for granted. The IDS instead lacks specific life cycle and organizational structures.