## 3 The Main Content and Key Technologies of SC Supported by DTs  
### Content Architecture and Key Technologies of DTs  
According to the adoption of DTs by NASA, DTs creates virtual bodies or digital models equivalent to physical entities [64]. Virtual objects can simulate and analyze physical entities and monitor the running status of physical entities according to the real-time feedback information of physical entities. According to the data of physical entities, the simulation analysis algorithm of virtual entities is improved. This provides more accurate decisions for subsequent operations and improvements of the physical entity [65; 66]. DTs are a comprehensive use of perception, computing, modeling, and other information technologies to describe, diagnose, and make decisions on physical space and then realize the interactive mapping of physical space and digital space. It can achieve high-efficiency collaboration, low-cost trial, and intelligent decision-making through data drive, model support, software definition, accurate mapping, and intelligent decision-making. It is suggested that DTs are a dynamic copy of the whole life cycle of entities or logical objects in digital space. It can realize digital representation, simulation tests, and prediction of object state and behavior with high fidelity using rich historical and real-time data and advanced algorithm models. [PERSON] et al. [67] suggested that the effective integration of DTs and lean construction is the key to the success of the project. DTs-based industrial construction has both digital and logistics production lines. The behavior model is first parameterized in the virtual body model establishment, transforming the change in material properties and mechanical properties into the form of parameter change. In addition, the rule model is parameterized. From the perspective of the physical model, the possible parameter changes of behavior and rule level are modularized in the finite element analysis software, and a dynamic DTs library is established. Finally, the whole process is simulated through multilayer model fusion using the DTs library as the driving force. DTs systems cover six core technologies, namely, perceptual control, data integration, model construction, model interoperation, business integration, and human-computer interaction [68; 69; 70]. The first is perceptual control technology, which is capable of data collection and feedback control and is the entrance to the physical world and the outlet of the feedback physical world. The second is data integration technology that can realize the interconnection of heterogeneous devices and systems so that the physical world and the virtual space hosting DTs can seamlessly connect. The third is the model construction technology to achieve the mapping of physical entity shape and law. The simulation of physical entity shape and known and unknown physical laws is realized through the construction of a geometric model, mechanism model, and data model [71,72]. The fourth is model interoperability technology, which undertakes the task of integrating geometry, mechanism, and data models and realizes the transformation from building a \"static mapping physical entity\" to building a \"dynamic collaborative physical entity\". Fifth, business integration technology is the link of DTs value innovation, which can break through the value chain of the whole product life cycle, the whole production process, and the whole business process. The sixth is human-computer interaction technology. [PERSON] et al. [73] believed that workers could feedback control instructions to the physical world through friendly man-machine operation by integrating human factors into the DTs system, thus realizing full closed-loop optimization of DTs. As the basis of DTs, an algorithm is a new methodology to understand and transform the world. As DTs are more and more closely related to social life and production, the algorithm has a more profound impact on society.