# A Systematic Review of the Trends and Advances in IFC Schema Extensions for BIM Interoperability
## 5 Evaluation of IFC Schema Extension Cases
### Analysis of Extension Cases by Product and Process Representations
#### 5.3.1. Detailed Analysis of Extension Approaches in the Architecture Domain  
Table 4 shows extension cases in the architecture domain classified according to representations and extension approaches. Four cases defined new entities and their related properties to represent new elements (i.e., products), while the other eleven cases involved defining entities and properties to represent newly defined processes. There were no cases in which property extensions were used exclusively for products, whereas five cases existed for process representations. The following details the cases in the resultant groupings:  
1. Product-oriented representations: - Using entity and property extensions. Refs. [39; 40] extended entities to define spaces either for space application support or legal conformance analysis. Ref. [38] extended entities required to represent sensing devices, such as RFID and IoT, while ref. [41] defined entities and their related attributes for novel firefighting systems. These cases also naturally used sub-typing using object types and/or property sets to represent different categories within these devices and systems. 2. Process-oriented representations: - Using entity and property extensions. Refs. [42; 51] defined entities to represent sketches and 2D drawing information that would enhance the parametric modeling capabilities of BIM models. Ref. [34] extended entities and relationships to bolster the representation of structural engineering models and refs. [48; 49; 50] to facilitate O&M data management. Furthermore, with the increased availability of point cloud data in the architecture domain, ref. [44] created a new schema, named _IfcPointCloud_, to incorporate point cloud models within the IFC schema. Similarly, ref. [45] formulated entities and related properties to characterize feature relationships intrinsic to module design processes, catering to the growing interest in modular buildings. Another characteristic of process representation was to extend entities via subtypes of _IfcRelationships_ (to _IfcObjectDefinition_) to specify new procedures. For example, ref. [43] introduced new relationship entities, such as _IfcRelElementChange_ and _IfcRelFeatureChange_, to monitor changes in BIM models during the design phase, thereby facilitating version management during IFC information exchanges. The MEP sector was also addressed by [56], who introduced entities and defined specific properties to facilitate control functions, such as managing heating curves and setting time schedules for air handling. Using property extensions (exclusively). Six of the studies only extended the schema by defining property sets and/or using sub-typing. Ref. [46] incorporated architectural design guideline details as property sets \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Domain**} & \multirow{2}{*}{**Sector**} & \multirow{2}{*}{**Objective**} & \multicolumn{3}{c}{**Main Purpose**} & \multicolumn{3}{c}{**Extension Approach**} \\ \cline{3-8}  & & & **Product** & **Process** & **Entity Extension** & **Example** & **Property Extension** & **Example** \\ \hline \multirow{5}{*}{Infrastructure} & \multirow{2}{*}{Harbor} & Define components for quay walls & O & & O & _IfcQuay_ & O & Link predefined properties in bsDD \\  & & [18] & & & & & & & bsDD \\ \cline{1-1} \cline{2-8}  & \multirow{2}{*}{Plants} & Define components for wastewater treatment plants [19] & & & & & & & \\ \cline{1-1} \cline{2-8}  & & Define components for river facilities [96] & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._and ref. [47] formulated property sets to capture concepts for construction cost estimation. Likewise, refs. [52; 53; 54] introduced supplemental property sets for building code compliance. Similarly, ref. [55] expanded the schema to incorporate sensor data from IoT sensor networks into the BIM model. Instead of defining additional property sets, they further delineated enumeration types for the _IfcSensor_ entity to link with existing property sets more precisely.