# BIM-Based Description of Intelligent Transportation Systems for Roads
## 4 BIM-Based Description of ITS for Roads
### Validation of the IFC Schema Extension  
In this subsection, to validate the IFC schema extension, the ITS scenario presented in Figure 5 is described in compliance with the IFC schema. Using the test software introduced above, the validation process is devised for checking whether the IFC schema extension precisely models BIM-based simulations of ITS for roads. For this purpose, the IFC model that corresponds to the ITS scenario shown in Figure 5 is created as an instance of the IFC schema extension, using the newly-defined entities, property sets, and the enumeration data type. The standard for the exchange of product model data (STEP) defines a data format for the IFC model [58]. Listing 2, as described below, shows an extract of the  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Name** & **Type** & **Description** \\ \hline _CommunicationType_ & P\_ENUMERATEDVALUE/IfcLabel & Property enumerators are V2V, V2I, and I2I communication types \\ _CommunicationChannel_ & P\_BOUNDEDVALUE/ IfcReal & ITS-G5 transmission channel specifications \\  & & based on ETSI EN 302 663 Standard [51] \\ _CommunicationDuration_ & P\_LISTVALUE/ IfcTimeMeasure & Duration of specific communication sessions \\ \hline \hline \end{tabular}
\end{table}
Table 2: Property set _Pset_DistributionSystemTypeITSC_ for describing _IfcDistributionSystem_ entities of type _COMMUNICATION_.  
STEP-based IFC model used for the validation process. For greater clarity and transparency, obligatory attributes, such as the global identifiers, are removed from the IFC model shown in Listing 2.  
...  
#1= IFCROAD(\$,\$,'HA9',\$,\$,\$,\$,\$,\$,\$,\$);  
#2= IFCROADITS(\$,\$,'HA9_TestField',\$,\$,\$,\$,\$,\$,\$);  
#3= IFCISSTATION(\$,\$,'V1',\$,\$,\$,\$,\$,\$  
ITS stations _V2_ and _RSUI_, respectively. Finally, the _IfcRelDefinesByProperties_ relationship entity is used to link each property set to the respective object entities (#18 and #25). Last, but not least, relationship entities (#33 to #37) define links between object entities (#1 to #6). The _IfcRelAssignsToGroup_ relationship entity is used to specify links between object entities of type _IfcTSStation_ and _IfcRoadITS_. For example, the ITS station _V1_ object ( #3) is integrated in the ITS network and linked to the _HA9_TestField_ object (#2) using the _IfcRelAssignsToGroup_ relationship entity (#33), representing ITS communication between two objects. The _IfcRelServicesBuildings_ relationship entity denotes the link between object entities of type _IfcTSSoad_ and _IfcRoad_. Figure 8 shows a visual representation of the IFC model of the ITS scenario.  
Similar to the steps described above, the STEP-based IFC model is verified using the test software, which runs syntactic and semantic checks on the IFC model based on the IFC schema extension previously verified. The test software investigates the IFC model against syntactic and semantic requirements specified by the official IFC certification program. Several criteria, such as formal compliance with the STEP conventions and the conformance of data with the IFC schema extension are examined. It can be concluded from the results that the proposed IFC schema extension is capable of describing intelligent transportation systems in terms of IFC models. The IFC models represent correct information of scenarios in intelligent transportation systems for roads, providing a robust formal basis for designing simulation platforms and defining various ITS applications.