## 2 Data Schema
### Inventory System and Code System  
According to the design conditions, the primary criteria and features of structural members can be formed into a systematic data schema. These relative values help engineers in classifying appropriate structural types and create a premise for managing bridge geometry as well as the subsequent structural diagram. After determining the desired bridge, such as three-span or multiple-span and gravity-anchored or self-anchored bridges, engineers can further classify the structure and orient the primary parameters of each structural member. Figure 1 shows an example of the structural classification of a general suspension bridge.  
Using the aforementioned structural type classification of bridges, the bridge inventory system can be created. Each structural member is classified into a category in the inventory system according to its functions or services within the bridge system. It may typically be inventoried as a superstructure (such as slabs, stiffening girders, cables, and expansion joints) or as a substructure (such as bridge piers, abutments, and bearings). It should be noted that to pre-define the characteristics of each category, the structural elements should either have similar features and properties in one category or be further categorized into specific hierarchical categories. As a 3D information model is defined separately following the concept of the object-based specification. For this purpose, each structural member in an inventory system's category must be assigned a particular identification (ID). The final  
Figure 1: Example of a structural classification for suspension bridges.  
information model is created by assembling the particular IDs of all the members obtained using their orientation data, including the coordinates and information constraints. In this regard, a detailed code system, i.e., a naming convention for each structural member, should be adopted. Following ISO 19650, the identification of information containers within a common data environment was proposed [26; 27].  
For each structural member, the identification consists of four classes (Figure 2). The first class includes general information regarding the \"project\" identifier and the \"originator\" of the information. With the initiation of a project, a single and independent common project identifier name is formed, which should be recognizably distinct from any individual project of any organization joining the project; otherwise, it should be defined as a sub-project. In addition, these joint organizations need an identifier name, which is included in each structural member ID to identify the individual responsible for producing this member information. The second class consists of information regarding the physical scope of each structure. The \"Volume/system\" identifier helps engineers in orienting the development of structural members in the horizontal direction, while the \"Level/location\" identifier helps assess the elevation of a member. The third class defines the purpose of the structure; the \"Type\" identifier should be defined for each type of information in order to orient the type of information that will be contained within the member. The \"Role\" identifier denotes the scope of the project assigned to an organization. The last class comprises a detailed code; it is divided into two fields: one that identifies the name of the structure (such as \"01\" for pylon and \"02\" for main cable) and another that identifies the exact member (such as \"01001\" for the left pylon and \"01002\" for the right pylon.) In each field, the detailed code should be a sequential number, similar to a series of structural members.