## 2 Background and Related Work
### FIWARE as a Reference Architecture for a Smart Industry
Figure 1 shows how FIWARE as RA can easily integrate as reference middleware to support the communication between CPS, external systems, and the components that act as actuators on the shop floor. Existing Similar Solutions: An Overview of Current Approaches to Address Semantic Interoperability Fragmentation and Their Limitations  
Currently, there are many efforts in research trying to address the different requirements of Industry 4.0 in such a complex and heterogeneous domain as industry, and we have selected those solutions that could be potential direct competitors of the FIL proposed software. Table 1 summarises the approaches of our main competitors, while Table 2 analyses their primary limitations based on a literature review in three specific domains: ease of integration, data management efficiency, and implementation cost. These domains are essential requirements for our proposed solution. Following Table 1, Table 2 delves into the interoperability challenges addressed by each approach, outlining their specific limitations. It further illustrates how the FIL component surpasses these constraints, offering a more robust solution to interoperability issues within the context of Industry 4.0. Within the context of Industry 4.0, a critical challenge is the fragmentation of semantic interoperability. Addressing this, our research introduces the FIL component, designed to bridge these gaps. FIL is rooted in principles that are integral to system engineering and \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Approach Category** & **Approach** & **Solution Overview** \\ \hline \multirow{4}{*}{Based on OPC-UA} & OPCUA-IPE & This approach leverages the OPC UA standard to address interoperability, focusing mainly on syntactic issues [48]. \\  & REST-based OPC UA middleware & This approach combines OPC UA with a REST-based middleware, aiming for flexibility in data integration across platforms [49]. \\  & Semantic Validation rules & High-level approach to represent and (semi-)automatically extracting formal rules from unstructured standard documents [50]. \\ \hline \multirow{4}{*}{Based on the IEEE 1451 Standard Standard} & IEEE 1451 Standard Transformation & This solution relies on the IEEE 1451 standard to achieve semantic interoperability, offering a specific service to facilitate external communication via JSON-LD structures [51]. \\  & Model-Driven Digital Thread & This solution extends the IEEE standard using RESTful APIs [52]. \\ \hline \multirow{4}{*}{Based on Semantic interoperability principles} & eWoT & The approach provides a SPARQL query-based mechanism to transparently discover and access IoT devices that publish heterogeneous data [53]. \\  & OPC UA Standard over TSN & Specialized middleware in general layered architecture [54]. \\ \cline{1-1}  & OPC UA Standard over TSN & The main focus of this component is on the communication from field devices implementing an OPC UA server to FIWARE, allowing communication with the FIWARE Orion Context Broker [55]. Currently is the de facto standard for implementing FIWARE-based solutions in industrial settings. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of current research solutions. The table summarises those software solutions that address similar challenges and/or approaches followed by our proposal of interoperability bridge. Figure 1: High-level logical architecture example, using FIWARE as middleware [47]. software development, offering a novel approach in comparison to existing methodologies. These principles not only address current interoperability challenges but also align with broader technological concepts, ensuring FIL's relevance and applicability in diverse industrial scenarios. Although existing solutions make meaningful contributions to specific facets of interoperability, they often incur high implementation and operational costs.