## 1 Introduction
### Technologies and Frameworks for Scalability Towards Industry 4.0  
According to [19], scaling from I3.0 to I4.0 is feasible, compatible and implementable with any of these reference frameworks: Smart Grid Architecture Model (SGAM), Industry 4.0 Architectural Reference Model (RAMI 4.0) and Industrial Internet Reference Architecture (IIRA), but it is crucial to deepen applied research in the different domains that constitute these references so that new challenges and solutions will emerge. In addition, Reference [20] emphasizes that the synergy and implementation of modern and advanced technologies for manufacturing 4.0 are essential, such as manufacturing execution systems (MESs) [21], fog computing systems [22], cloud computing systems suitable for enterprise resource planning (ERP) applications [23], cognitive digital twins (CDTs) [24] and all those technological pillars that fit along the entire value stream of production 4.0. In keeping with this, techniques and practical approaches from other studies were investigated to provide insight into the integration of advanced technologies in a classical industry for scaling up to I4.0 and also under a RAMI 4.0 framework. Under an SRL, there are integrated technologies such as digital twins (DTs), data management in an ERP system, roadmaps and service design methodologies; however, there are issues that have not been investigated such as security and ensuring that the required infrastructure and technologies are well integrated. Reference [25] mentions in the review article that there is no clear and uniform definition of what digital twins (DTs) are, especially in the context of referential models, to ensure a coherent understanding and application in industrial digitization; in addition, [26] proposes the development of ontologies and knowledge graphs of DTs. Reference [27] supports RAMI 4.0 as a guide for the implementation of an IBPT concept that integrates ITs and OTs such as a service-oriented architecture (SOA) and the use of the OPC UA standard, together with advanced augmented reality (AR) and natural language processing (NLP) interfaces, in a simulated production environment, although its implementation complexity and dependence on a robust infrastructure could limit its applicability in certain industrial contexts, such as MSMEs or SMEs. Likewise, in [28], the authors scale an I3.0 to I4.0 SME company based on the reference model guide when implementing a machine-human interface (HMI) in the production line, in order to digitize the acquisition of production data and integrate them into an ERP (enterprise resource planning) system. On the other hand, Reference [29] developed a platform under the RAMI 4.0 reference model for a user to visualize and manipulate the systems and processes of Industry 4.0. These services were constituted by means of a service-oriented architecture (SOA) and the OPC UA communication protocol. Reference [30] make it clear that the applicability of a referential model in a real industrial environment can provide a clear roadmap towards digital transformation. Despite this, their evaluation methodology noted that the successful implementation of the standards covered by the reference model is complex, due to the availability of limited technological infrastructure, investment in new technologies, training of skilled personnel and organizational adaptation.