# Reference Models for Digital Manufacturing Platforms
## 2 State of the Art  
Reference models for I4.0 is a novel research field that requires special attention in new Internet and cyber-physical paradigms for manufacturing. For the most part, reference models for I4.0 are based on the Computer Integrated Manufacturing Open System Architecture (CIMOSA) [17] and the ISA 95 standard [18], at least to some extent. CIMOSA is an event-driven approach to model enterprise processes in an integrated computerized framework [17]. ISA 95 is an architectural model to facilitate the integration of the enterprise functions and control systems. It provides a hierarchical structure of the manufacturing systems from production processes to a higher level, i.e. business logistics [18]. The Reference Model for Industrie 4.0 (RAMI 4.0) [19] is a unified architectural reference model that provides a collective understanding for I4.0 standards. It can be regarded as a tool to map I4.0 concepts and use cases. In RAMI 4.0, I4.0 components are defined in their structure and functions. The model provides an orientation for plotting the requirements of use cases in order to define and further develop I4.0 concepts and products. RAMI 4.0 is based on the Smart Grid Architecture Model (SGAM) [20], a model developed for purposes of communication in networks of renewable energy sources [21], which seems suitable for I4.0 applications as well. The National Institute of Standards and Technology (NIST) promotes the Smart Manufacturing vision [22] as a fully integrated, collaborative manufacturing system able to cope with the challenges for quality, efficiency, and personalization that manufacturing companies are facing today. Through the adoption of NIST Smart Manufacturing standards, small-to-medium sized companies can implement this vision, benefitting from public documentation, reference software implementations, and conformance testing. China's National Intelligent Manufacturing System Architecture (IMSA) [23] is the response of the State Council of the People's Republic of China to foster the standardization works that will guide the upgrade of Chinese manufacturing towards intelligent manufacturing. Developed by the Ministry of Industry and Information technology of China (MIIT) and the Standardization Administration of China (SAC) [24], and presented in the Made in China 2025 document, the intelligent manufacturing concept involves the integration of new information technology, new materials, numerical control tools, novel equipment, and machinery as key areas to support the development of the Chinese economy. IMSA is basically a guideline for the construction of standards to facilitate the interconnection of manufacturing processes since this interconnection and interoperability are regarded as the key drivers to materialize the intelligent manufacturing concept. The Industrial Internet Reference Architecture (IIRA) for Industrial Internet of Things (IIoT) Systems [25] was first published in 2015 by the Industrial Internet Consortium (IIC) Task group. Consortium members include systems and software architects, and business and security experts in different IIoT application domains, mainly Energy, Healthcare, Manufacturing, Public Domain, and Transportation. The reference architecture enables IIoT system architects to design their own systems using a common vocabulary, a standard-based architecture framework, and reference architecture. These follow the ISO 42010 System and software engineering architecture standard [26], where the architecture of software systems is described, analyzed, and defined to solve specific concerns from the viewpoint of different stakeholders. Similar to IIRA, the IEEE Standard for a Reference Architecture for Smart City (RASC) [27] is another reference architecture for IoT systems based on ISO 42010 in the domain of smart cities.