# Reference Models for Digital Manufacturing Platforms
## 5 Conclusions  
This paper presents an analysis of different cutting edge reference models and architectural reference models for digital manufacturing platforms. They provide, in many cases, complementary views on digital manufacturing platforms, and, in general, it is rather straightforward to align the definitions they contain. The RAMI 4.0 reference model contains the specifications of the administration shell, which can be regarded as a standardized digital representation of a manufacturing asset providing interfaces to interact with it. The analysis showed that the level of maturity of RAMI 4.0 is the most advanced among the different reference models under analysis. Besides this, there are several alignment reports available between the RAMI 4.0 and other reference models, which make it easier to extrapolate any mapping to RAMI 4.0 to the other reference models. Therefore, RAMI 4.0 has been selected as the reference model for analysis, and the different alignment reports have been used to complete the analysis. It is important to note that the alignment between the RAMI 4.0 and the Smart Manufacturing Ecosystem from NIST has been specifically developed as part of this research work. The main divergence between the different reference models is found in the standardized protocol stacks and data formats to exchange data. This is an important aspect which has to be taken into consideration in the design of any digital manufacturing platform, concerning inter-platform communication and IIoT data acquisition. In this sense, it is recommended that system components, mainly IIoT data acquisition and data transformation, incorporate technologies to deal with high levels of diversity in edge communications networks. Based on this alignment, and in order to give response to the need of a more complete and integrated reference model for the design and implementation of the ZDMP Platform, the paper presents the Industrial Internet Integrated Reference Model (I3 RM) and non-binding recommendations to align the global architecture definition, functional specifications, and technical specifications of digital manufacturing platform use cases to the guidelines and examples promoted by the different reference models under analysis. The recommendations provide a standard framework to structure the technical information generated in the use case, to support the design, implementation and validation of the system. Following these recommendations, interoperability will be guaranteed with state-of-the-art digital manufacturing standards and solutions. The paper also presents an extension of the three-tier architecture pattern. The different functional blocks of a digital manufacturing platform have been mapped to the RAMI 4.0 reference model to find out to what extent they are covered in this reference model. The main conclusion is that aspects regarding software development, application marketplaces, collaboration between developers, and collaboration between developers and users, are innovative aspects and it is necessary to extend the three-tier system architecture to better understand the requirements they imply. The three-tier global architectural pattern of IIRA has been extended with a new tier, named collaboration, to address this aspect. It is worth mentioning that this study involves some limitations. One limitation is related to the analysis coverage as the reference models alignment study only involves the cutting edge reference models for IIoT systems. However, there are other reference models such as IBM Industry 4.0 Reference Architecture that have not been included in the analysis. Further research could be focused on the alignment analysis of other reference models. Another limitation is related to the constraint of the analysis according to the specific dimensions of the studied reference models. Future research lines could be addressed to define a meta-reference model to map the reference model together with additional dimensions, such as social and sustainability.