# Scene Equipment Saving and Loading Method for Digital Twin Workshop
## 3 Materials and Methods
### Workshop Information and Saving/Loding Model Definition
#### 3.1.1 Workshop Element Information Model  
The data from the DT service system control the presence and operation of the equipment in the virtual workshop. Each workshop element contains two types of information: a 3D model and attribute behavior information, among which the 3D model is the external expression of workshop elements in the virtual workshop. This allows the workshop administrator to review them in an intuitive form, while attribute behavior information is used to describe the status and behavior of workshop elements; for example, the machine tool possesses attribute information such as the machine code, manufacturer, etc., and behavior information such as the machining action and working status. Figure 1 depicts the types of data contained in the various elements of the workshop. Based on the logical relations, the information about the workshop elements is divided into five levels from the inside out. Layer 1: DT Object. DT Object is an abstract concept used to describe the overall integration of all objects in the workshop. Workshop assets that can be digitally represented and can directly affect physical objects may be considered DT Objects. Layer 2: Workshop information base class. This is the base class of all objects contained in the workshop, and it contains three classes in total according to the type of workshop information: element class, viewer class and info class. It contains the basic functions, such as the ability to create and destroy the objects. The use of a unified abstract base class to manage the creation and destruction of objects, memory allocation and release can improve system performance and code reusability. Layer 3: Workshop information-derived class. Derived from the workshop information base class, it further elaborates the information type for the workshop element and initially specifies six major types of information contained in the workshop: machine tool, storage, transport, saved archive, fixed viewer and roam viewer classes. Layer 4: Workshop information-specific object. Due to the presence of numerous variations within the same major device category, they are abstracted into another layer. This is the most fine-grained shop equipment specific object, which can be defined based on the workshop information derived class and the actual workshop situation. Layer 5: Workshop information detail object. The information contained in the workshop information-specific object, which is mostly defined in the form of structures or fields within the concrete object class, is used to store the state and properties of the object. Such hierarchical classification allows for better management of extensive device information within the workshop. To elaborate on the relationships between the components of the workshop elemental information in more detail and with greater specificity, a formal description method is introduced to explain them. The symbols, meanings and schematic use cases for representing the relations between the components of the element information are presented in Table 2. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Symbol** & **Meaning** & **Use Case** & **Explanation** \\ \hline \(\in\) & belong to & Workshop equipment \(\in\) Workshop object & Workshop equipment belonging to workshop object \\ \(\rightarrow\) & inheritance & Machine tool class \(\rightarrow\) Element class & Machine tool class inherited from element class \\ \(>\) & instance & Lathe class \(>\) Machine tool class & Lathe class is an instance of machine tool class \\ \(:\) (_parantent_) & property & Machine tool: (_ID_, _Manufacturer_) & Machine tools have properties, such as their ID and manufacturer \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Schematic table of mathematical symbols and their use cases. Figure 1: Classification chart of workshop elements information model. As shown in Formula (1), the DT Object refers to all of the objects in the workshop, from which it is further divided into three workshop information base classes:  
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