## 2 Existing Studies
### Discussion  
Figure 2 summarizes and compares some closely related studies on relationship information establishment with the proposed approach. According to Figure 2, some methods were proposed for MEP logical relationships generation by 3D point clouds, but not IFC files or 3D CAD models. Some other studies focused on typological analysis with BIM or CAD model of the AEC industry, but they did not consider the specific characteristics of MEP components and MEP knowledge, which contributed to the logical relationships of MEP model. These approaches attempted to explore the intrinsic value of MEP components and to represent this information in a more rational and user-friendly format, which could be beneficial to a variety of FM practices. Although studies shown in Table 1 introduce the attempts of generating relationship information, the analysis of spatial topology and use of prior knowledge still requires a more intelligent and automatic approach. Otherwise, the generation of the logic chain for MEP systems is a repetitive, time-consuming and error-prone task for either repair technicians or equipment managers. In this study, a BIM-based topological analysis method, a query language identification and a MEP logical query engine within MEP systems are proposed to generate the logic chain automatically to improve the efficiency of FM. In the proposed approach, the connection tables are the results from spatial topology analysis, which provide the foundation for the generation of the logic chain; and identification rules are extracted from prior practical knowledge or user-defined rules, providing the foundation for logical inferences. The connection tables and MEP knowledge are two foundations of the MEP logical query engine for generating the MEP logic chains automatically.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Class**} & \multicolumn{2}{c}{**Relationship**} & \multicolumn{2}{c}{**Relationship**} & \multirow{2}{*}{**Platform**} & \multirow{2}{*}{**Geometric Data Source**} \\  & & \multicolumn{2}{c}{**Modeling**} & & & & & & & & \\ \hline \hline \multirow{3}{*}{**Sub-Class**} & \multirow{3}{*}{**Spatial**} & \multirow{3}{*}{**Logic**} & \multirow{3}{*}{**Manual**} & \multirow{3}{*}{**Automatic**} & \multirow{3}{*}{**Business**} & \multirow{3}{*}{**Self-Developed**} & \multirow{3}{*}{**IFC**} & \multirow{3}{*}{**3D**} & \multirow{3}{*}{**Clouds**} \\  & & & & & & & & Engine & & & \\ \hline [PERSON] et al. [28] & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & & \\ [PERSON] et al. [7; 35] & \(\bullet\) & \(\bullet\) & \(\bullet\) & & \(\bullet\) & \(\bullet\) & & & \\ [PERSON] et al. [16] & \(\bullet\) & & & \(\bullet\) & \(\bullet\) & & & & \(\bullet\) & \\ [PERSON] et al. [19] & \(\bullet\) & & & \(\bullet\) & & \(\bullet\) & & \(\bullet\) & \\ [PERSON] et al. [8] & \(\bullet\) & \(\bullet\) & \(\bullet\) & & \(\bullet\) & & \(\bullet\) & & \\ Proposed approach & \(\bullet\) & \(\bullet\) & & \(\bullet\) & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of methods for generating MEP relationships.