## 3 3D Interpreted Model
### Definitions and Characteristics  
The MBD dataset is used to completely define the relevant dataset of products, the core of which is the product model named MBD model. The MBD model includes a design model (3D geometric model) and its associated annotations and attributes. Among them, design model is the 3D graphical representation of product model; annotations refer to the dimensions, tolerances, notes and datum directly displayed in the 3D environment; and attributes are the information equivalent to annotations in content, but its form is text description and table. Because the product manufacturing information is integrated into the design model mainly by annotations and supplemented by attributes, the MBD model can be defined as 3D annotated model, and the product model formed by the integration and fusion of 3D annotated model and design knowledge is defined as 3D interpreted model. The overall process of product model developing from 3D geometric model to 3D interpreted model is shown in Figure 3.  
**Definition 1**. : _3D Annotated Model (3 DAM). 3D annotated model is a kind of product model, which takes the explicit annotation of product technical information in 3D environment as the main means, supplemented by a certain way of implicit information interaction, and can completely describe and define the geometric and technical information of a product._  
Figure 3: The developing process of the product model from a 3D geometric model to a 3D interpreted model. 3 DAM can be represented as follow. \[3 DAM=\left\{INF_{g},INF_{t}\right\} \tag{1}\]  
where, \(INF_{g}\) represents the product geometric information, such as model, surface, edge, etc. ; \(INF_{t}\) represents product technical information, such as dimensions, tolerances, roughness, datum, etc. In the 3 DAM stored in STEP, the geometric information is mainly combined into model geometry by boundary representation (B-rep). For example, the shape of the model is composed of faces and the face is composed of edges. The integration of technical information with geometric information is realized by forming a large number of association groups. For example, the feature control frame forms the association group with the controlled feature through arrows. 3 DAM has the following characteristics:  
* Information integrity. Information integrity means that product geometric information and technical information can completely define the product, and there is no missing or redundant product information. * Information consistency. Information consistency means that there is consistency between product technical information and there is no mutual exclusion between technical information. **Definition 2**. : _3D Interpreted Model (3 DIM). The 3D Interpreted Model is a kind of product model formed by integrating and fusing product design knowledge on the basis of 3 DAM, which can not only describe and define product geometric and technical information completely, but also integrate and control the design knowledge hidden behind product geometric and technical information._  
3 DIM has richer and more accurate semantic information and resource and can be represented as follow. \[3 DIM=3 DAM\cup DK=\left\{INF_{g},INF_{t},DK\right\} \tag{2}\]  
where, \(INF_{g}\) represents product geometric information; \(INF_{t}\) stands for product technical information; \(DK\) represents design knowledge. In this paper, design knowledge refers to the intellectual elements hidden behind the product model, such as design intent, design justification, design decision and design option. \[DK=\left\{DI,DJ,DD,DO\right\} \tag{3}\]  
where, \(DI\) refers to design intent; \(DJ\) refers to design justification; \(DD\) refers to design decision; and \(DO\) refers to design option. The specific meaning and examples of each type of design knowledge are shown in Table 1.