# Reference Models for Digital Manufacturing Platforms
## 4 Industrial Internet Integrated Reference Model
### Implementation Viewpoint  
The implementation viewpoint should provide details on how the AAS will be deployed to the computing infrastructure. The Platform Industrie 4.0 [49] describes different deployment patterns that can be used in a consistent IIoT System from different views: physical proximity, distribution, virtualization, and lifecycle:  
* Proximity: Physical proximity of the asset to the AAS. * Asset-Based: AAS hosted in asset's runtime environment. * Edge/Fog Based: AAS hosted in a computing environment in the local IT infrastructure of the enterprise. * Cloud Based: AAS hosted in cloud infrastructure. * Distribution: Distribution of AAS data elements and services across different runtime environments. * Centralized AAS: A 1 to 1 relationship between asset and AAS and unique entry point (e.g., URL) for the AAS. * Distributed AAS with Loose Coupling: Information for an asset under the same AAS and multiple entry points for the AAS, distributed based on the different organizations that need access to the different data elements. * Distributed AAS with Aggregating Node: An aggregating AAS provides a single access point to access all the information of the asset, collecting information from other lower level AAS distributed among collaborators. * Virtualization: Virtualization of the runtime environment of the asset. * Operating System: No virtualization. * Hypervisor Deployment: Runtime environment in virtual machines managed by a hypervisor. * Container: Container-based runtime environment (e.g., Docker). The implementation viewpoint needs to take into consideration the different trade-offs among these deployment patterns, also considering the IIRAs architectural patterns for a consistent IIoT system and the specific requirements of the use case. It is also important that the implementation is described in a format that effectively captures the selected deployment patterns. In this sense, one recommendation is to use a multi-layered approach to describe the implementation and selected patterns for the different system components, such as the C4 model [50]. The C4 model comprises four different levels of abstractions to visually communicate the system architecture: context, containers, components, and code. The first level of abstraction, context, shows a high-level description of the system being described, focusing on the user, user roles, and interactions with the systems. As indicated above, it is recommended to use the three-tier architectural pattern as a reference, but also to take into account the functional viewpoints to better describe the proximity network and the interactions between different hierarchical levels. In this sense, it is important to highlight that the three-tier-architecture pattern in IIRA (edge tier, platform tier, enterprise tier) might be insufficient to determine the system boundaries between different stakeholders in collaborative scenarios. In this sense, the RAMI 4.0 hierarchical level dimension is very convenient due to the differentiation between the Enterprise and Connected World levels. The three-tier architecture pattern is, on the other hand, very convenient for describing a consistent IIoT system architecture and deployment pattern. For this reason, the three-tier architecture pattern is extended with a four tier, collaboration tier, to highlight the boundaries between the different private (cloud) systems in a collaboration network. Figure 10 illustrates the mapping of a digital manufacturing platform, the Zero Defect Manufacturing Platform (ZDMP), to the proposed four tier architecture pattern. The ZDMP platform provides a marketplace and Software Development Kit (SDK) to develop applications to realize the zero-defects manufacturing paradigm in manufacturing companies [51]. The ecosystem is supported with a portal and engagement hub to promote the collaboration between stakeholders (mainly software developers and manufacturing companies).