## 2 Literary Review and State of the Art
### RAMI 4.0 (Reference Architectural Model Industry 4.0)  
RAMI 4.0 is a three-dimensional reference model that organizes and structures the key elements of Industry 4.0, facilitating integration and interoperability between industrial and digital systems. This model covers aspects from physical assets to business processes, including communication, information management and function orchestration. The referential model enables industrial systems to evolve towards more flexible, scalable and adaptable architectures, supporting the transition from traditional plants to smart and connected environments. In an Industry 4.0 project, the adoption of reference model ensures that all components, from plant hardware to cloud services, are aligned and operate cohesively to achieve the goals of efficiency, quality and resilience.  
The Architectural Reference Model for Industry 4.0 is illustrated as a three-dimensional cube that integrates all key aspects necessary for the implementation of Industry 4.0. This model is organized along three axes: the hierarchical axis, the layer axis and the lifecycle and value chain axis. The hierarchical axis, based on the IEC 62264 (44) and IEC 61512 standards (45), runs from the 'Product' to the 'Connected World', representing different levels of the automation hierarchy, from field devices to cloud integration. The layer's axis spans six levels: Assets, Integration, Communication, Information, Functional and Business, each detailing a crucial aspect of industrial systems, from physical components to business processes. The lifecycle and value chain axis, supported by the IEC 62890 standard (46), considers the phases of development, use, maintenance and, finally, decommissioning of a product or system, dividing these phases into 'Types' and 'Instances'. 'Types' are associated with the development and use/maintenance stages, representing general or abstract definitions of a component, such as templates or theoretical models. On the other hand, the 'Instances' relate to the production and use/maintenance stages, indicating the concrete and specific implementations of these models in reality, for example, a particular device in operation in a factory, i.e., these phases allow the model to cover both the theoretical design phases and the practical implementation, facilitating the management of the complete lifecycle of products and systems within the Industry 4.0 environment (35).  
Despite this, it must also be said that the RAMI 4.0 reference model does not elaborate how the parts within this complex solution space are interconnected and interact, nor does it consider the different actors involved, who may sometimes have conflicting interests. In other words, it is not clear how the new generation standards can implement a data-driven architecture (Digital Thread) that links the information generated throughout the product lifecycle.  
In Table 1, a synthesized view of the technological approaches in Industry 4.0 is shown, facilitating a clear and quick understanding of their advantages and limitations without requiring an exhaustive analysis of each source. It also highlights the strengths where it introduces innovations or solves common problems in previous research, thus allowing a better contextualization of its relevance in the field.