## 3 Digital Twin, from Concept to Architecture Model
### Classification of Digital Twins
Modeling the information regarding a device, production unit, or plant, generally called an \"asset\", across it's lifecycle, through digital representation, has been used by industrial manufacturers, but still it has no Digital Twin significance. Nowadays, Digital Twin's added value, which extends the capabilities of information models, is mainly related to digital technology improvements, architecture development, standardization, new use cases, interactions, and business models facilitated by the Digital Twin (Table 3). In many Digital Twin use cases, it is required to store data externally, for example, in the Cloud, so it is necessary to have high-speed and reliable connectivity to the manufacturing processes, assets, and operators. Adequate security capabilities are important for data acquisition, exchange, control, and management. Some processes and products offer the possibility of realizing their digital twins, as an isolated solution. However, many use cases rely on interactions between several digital twins offered by different companies. These points highlight the necessity of Digital Twins interoperability and related data management, synchronization, and exchange. Based on these technologies, digital twins can enable new use cases such as real-time simulation of production systems, information exchange across the manufacturing chain, predictive product design, efficient commissioning of devices and plants, analytics, and manufacturing [17]. \begin{table}
\begin{tabular}{l l l l} \hline
**Classification Criteria of DTs** & **Types of DTs** & **Selected References** \\ \hline \multirow{2}{*}{Depending on the time of creation} & \(\bullet\) & Digital Twin Prototype (DTP) & [12] \\  & \(\bullet\) & Digital Twin Instance (DTI) & \\ \hline \multirow{3}{*}{Depending on the integration level} & \(\bullet\) & Digital Model & \multirow{3}{*}{[13]} \\  & \(\bullet\) & Digital Shadow & \\  & \(\bullet\) & Digital Twin & \\  & \(\bullet\) & Predictive DT & \\ \hline \multirow{2}{*}{From the application point of view} & \(\bullet\) & Predictive DT & \multirow{2}{*}{[12]} \\  & \(\bullet\) & Interrogative DT & \\ \hline \multirow{3}{*}{According to the parameters on which the application focuses} & \(\bullet\) & Product DT & \multirow{2}{*}{[12,14]} \\  & \(\bullet\) & Production DT & \\  & \(\bullet\) & Performance DT & \\ \hline \multirow{3}{*}{From a hierarchical point of view} & \(\bullet\) & Unit level & \multirow{3}{*}{[12,14]} \\  & \(\bullet\) & System level & \\ \cline{1-1}  & \(\bullet\) & System of Systems (SoSs) & \\ \cline{1-1}  & & level & \\ \hline \multirow{3}{*}{Depending on the level of maturity} & \(\bullet\) & Partial DT & \multirow{3}{*}{[15]} \\  & \(\bullet\) & DT Clone & \\ \cline{1-1}  & \(\bullet\) & Augmented DT & \\ \hline \multirow{3}{*}{Functional sophistication level of the virtual representation} & \(\bullet\) & Pre-Digital Twin, & \multirow{3}{*}{[16]} \\ \cline{1-1}  & \(\bullet\) & Digital Twin & \\ \cline{1-1}  & \(\bullet\) & Adaptive DT & \\ \cline{1-1}  & \(\bullet\) & Intelligent DT & \\ \hline \end{tabular}
\end{table} 
Table 2: Classification of DTs adapted from [11].