## 3 Digital Twin, from Concept to Architecture Model
### Digital Twin Models, Frameworks, and Architectures
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Characteristics** & **[PERSON] et al. [18]** & **[PERSON] et al. [19]** & **[PERSON] et al. [23]** \\ \hline \multirow{2}{*}{Application Field} & Smart manufacturing, convergence of digital and physical space & Cloud-based cyber-physical systems, telematics application & Industrial transformation, mass individualization \\ \hline \multirow{2}{*}{Technologies and methods used} & Technologies for data processing and information model & Cloud computing, Bayesian network, fuzzy logic & Cloud computing, Internet of Things, augmented reality, ThingWore, Vutoria \\ \hline \multirow{2}{*}{Key aspects} & Data-driven smart manufacturing, smart decisions at every manufacturing point & Telematics-based driving assistance & Real-time monitoring, Remote controlling, Prediction \\ \hline \multirow{2}{*}{Architecture model} & Proposes a reference model for DT in the context of smart manufacturing & Reference model for C2 PS architecture & Adopts RAMI and an agile model for integrating different levels of DT \\ \hline \multirow{2}{*}{The relationship with Industry 4.0} & Integrating DT in smart manufacturing operations & Integrating cloud computing and physical sensor level control & Use of Industry 4.0 technologies \\ \hline \multirow{2}{*}{Data source} & Capturing information from physical devices and their integration into the manufacturing process & Capturing information from physical devices & Integration of data from various sources \\ \hline \multirow{2}{*}{Adaptability} & Adaptability to varied production needs & Adaptability to environmental changes & Adaptability in deployment and integration \\ \hline \multirow{2}{*}{Security} & Implementing security measures and controls in the context of smart manufacturing & Implementation and compliance with security strategies for data in Cloud & Use of security technologies in DTaaS \\ \hline \multirow{3}{*}{Interoperability} & Compliance with ISO standards and compatibility with existing systems & Integration with other systems and compliance with standards & Agile approach for different levels of integration \\ \hline \multirow{3}{*}{Challenges and future research directions} & Standardization of communication protocols, real-time data processing, timeliness and accuracy of models, reliability & Scalability and the realization of interactions between systems, integration with Blockchain and artificial intelligence & Integration levels, mass individualization, resilience of the Digital Twin \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of architectures adapted from [18; 19; 23]. module of the Digital Twin services at the cyber level, thus facilitating the integration of the sensor-service fusion module. In ref. [24], [PERSON] et al., proposed the use of methods to ensure the progress of Digital Twins by building a global model through which the common characteristics of the systems and the intrinsic relationships at the data level are identified. The proposed approach contributes to the improvement of the prediction accuracy of the DT model accuracy. Based on the global model, a personalized model can be developed, using the multi-tasking learning principle. This principle's benefits have been extensively presented in [25]. The meta-learning model examines the adaptation of the global model using the principle of \"fast learning\" through the use of a reduced quantity of training data. This principle is presented in [26]. Using the meta-learning model does not ensure performance at the system level but provides advantages in relation to specific tasks. Another model of the life cycle presented in [10], assumes the structuring of the DT on three components: physical space, the data processing layer, and the digital space (as shown in Figure 9). In ref. [10] an application framework is presented. The physical space represents a dynamic environment of production that comprises people, machines, materials, and rules.