## 2 Background
### IT/OT Convergence  
In the I4.0 perspective, the fully connected factory concept is a key technology enabler for manufacturing operators to drive the production environments up to an expected development, impacting both the IT and OT layers. The technological improvement of the industrial IoT (IIoT) brings new highly reliable devices with advanced built-in communication capabilities, since new state-of-the-art devices, together with the work machines operating at production sites, generate a huge amount of data. Any division of the organization, from design departments to shop floors, provided with adequate access permission, can take advantage of this unprecedented data depot. The attainment of most goals of the I4.0 transition is bound to the gradual integration of algorithms used by manufacturing machines with information about the surrounding infrastructure. In the literature, this trend is referred to as IT/OT layer convergence, which denotes the decrease in the gap between the manufacturing processes in the shop floor on the one hand and the IT department resources (e.g., storage, networking, and computing facility) on the other. IT/OT convergence is a topic covered by most authoritative standardization bodies, such as the International Society of Automation (ISA) [14] and the International Electrotechnical Commission (IEC) [15]. In particular, the multi-layer IEC 62264 standard based on the ISA-95 specifications [16] defines an information exchange framework model for enabling the integration of applications running in business and operational departments. Enterprises complying with that standard can define interfaces between control and business functions, allowing them to make informed decisions on the data to exchange so that costs and risks can be kept low in case of implementation errors. The US Industrial Internet Consortium (IIC) [17] proposes the Industrial Internet Reference Architecture (IIRA) [18] as guidance in developing smart IIoT architectures. The specification strongly stresses the concept of convergence of the IT and OT layers at various levels, underlining the common requirements for tackling the transition from an industrial perspective with proper computer architectural patterns. Other authoritative standards, like the European Reference Architectural Model Industrie 4.0 (RAMI 4.0) [19] and the Chinese Intelligent Manufacturing System Architecture (IMSA) [20], push toward a tighter integration of IT and OT. RAMI 4.0 and IMSA are comprehensive models proposing high-level reference architectures, addressing all Industry 4.0 concepts. The concept of the I4.0 component is of particular interest in the vision depicted by the RAMI 4.0 specification [21]. This concept highlights how the smart factories embracing the I4.0 transition will have smart objects as main actors, with industrial equipment outfitted with the right level of intelligence to allow secure control coming from the highest tiers of architecture (i.e., the managerial ones). Furthermore, the communication layer of the RAMI 4.0 specification connects the I4.0 scenario to a key standard sketching many implementation directions, namely Open Platform Communications Unified Architecture (OPC UA) [22; 23; 24]. The OPC UA [25] produced by the OPC foundation [26] collocates in the panorama of I4.0 standard initiatives as a concrete effort to propose low-level and technical specifications. The OPC UA defines a standard set of objects and interfaces, facilitating the interoperability among control processes and manufacturing automation applications [25]. The many challenges of the I4.0 transition forced the OPC foundation to think about the heterogeneity of software and hardware components by proposing a unifying architecture tackling these diversities, namely the Unified Architecture (UA) specification [26] released in 2006 and what become the IEC-62541 standard [27].