# BIM-Based Description of Intelligent Transportation Systems for Roads
## 4 BIM-Based Description of ITS for Roads
### An IFC Schema Extension for ITS for Roads
The IFC schema defines different distribution system types using the enumeration type _IfcDistributionSystemEnum_, listing enumerators such as _SIGNAL_, _DATA_, and _COMMUNICATION_. For describing communications in the ITS domain, _IfcDistributionSystemEnum_ of type _COMMUNICATION_ is further specified using the property set _Pset_DistributionSystemTypeITSC_ introduced in Table 2. As ITS communications are a variation of communications in cyber-physical systems, recommendations from [55] have been taken into consideration for developing the property set _Pset_DistributionSystemTypeITSC_. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Name** & **Type** & **Description** \\ \hline _SensingResource_ & P\_LISTVALUE/IfcLabel & A list of all sensors attached to ITS stations, e.g., MEMS, LiDAR sensors, RFIDs, cameras, and temperature sensors \\ _ComputingResource_ & P\_SINGLEVALUE/IfcLabel & Description and specification of the on-board computing unit \\ _PowerResource_ & P\_SINGLEVALUE/IfcLabel & Description and specification of the on-board power unit \\ _CommunicationResource_ & P\_LISTVALUE/IfcLabel & Description and specification of the on-board computing unit \\ _AcuatingResource_ & P\_LISTVALUE/IfcLabel & A list of all actuating units, if existing, attached to ITS stations, such as dampers and automatic crossing barriers \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Property set _Pset_ITSSResources_ for describing _IfcTTSStation_ entities. The objectified relationship _IfcRelAssignsToGroup_ assigns object definitions to a group. Here, instances of the _IfcItTSStation_ entity (_RelatedObjects_) are assigned to instances of the _IfcRoadITS_ entity (_RelatingGroup_). Last, but not least, for connecting the _IfcRoad_ entity as a spatial element to the _IfcRoadITS_ entity, the objectified relationship _IfcRelServicesBuildings_ is used. Listing 1 shows an extract of the extended IFC schema with entities relevant to ITS for roads denoted in EXPRESS. ```
... TYPEIfcITSSStationTypeEnum=ENUMERATIONOF (VEHICLEUNIT,PERSONALUINIT,ROADSIDEUNIT,CENTRALUUIT,USERDEFINED,NOTDEFINED); END_TYPE; ENTITYIfcITSSStation SUBTYPEOF(IfcDistributionElement); StationID:IfcInteger; HasActuator:IfcBoolean; StationType:IfcITSSStationEnum; END_ENTITY; ENTITYIfcRoadITS SUBTYPEOF(IfcDistributionSystem); END_ENTITY;...
```  
The IFC schema extension is verified with respect to syntactic, semantics, and unit check criteria using the test software of the official IFC certification program [56; 57]. The test software verifies the IFC schema extension according to EXPRESS syntax specifications, such as compliance to notational conventions, declarations of entities and data types, and declarations of entity attributes and functions. Moreover, since the syntactic criteria are met, the test software is able to generate Java classes for newly defined entities and enumeration data types. In this study, the test software confirms that no domain rules are violated and that the proposed IFC schema extension has successfully passed the verification test. Therefore, the proposed IFC schema extension can be used to create BIM-based models of ITS for roads in compliance with IFC syntax and semantics.