## Extended IFC-Based Information Model Creation Method  
### IFC Extension for Railway Track Object Representation  
Information management is an essential aspect to consider when using BIM. The information is stored and managed in different ways because the same information is used for different purposes by the users. In this study, IFC was used to integrate and manage the information similarly. IFC entities for each element are essential for creating IFC-based railway track information models that facilitate interoperability. However, it is difficult to represent railway track elements because IFC4 \(\times\) 2, which is the latest IFC version, does not contain elements, such as sleepers and ballasts, which are still under development. Therefore, the entities in this study were extended, according to the basic rules of IFC, to represent railway track elements in addition to alignment. The schema to be applied to railway track information models was extended following the research of [PERSON] et al. [33], who referred to the China Railway BIM Alliance [6] and Korea Rail Network 3 Authority (KR) [34]. Figure 4 illustrates the IFC entities extended in this study through EXPRESS-G diagrams. The IFC entities extended for railway track element representation can be primarily classified into physical entities, which contain information regarding track elements, and spatial entities, which contain information regarding space. The physical entities were represented as \"IfcTrackElement\" under \"IfcCivilElement\", which was created for the extension of infrastructure elements in IFC4 \(\times\) 2; the spatial entities were represented as \"IfcTrackStructureElement\" under \"IfcCivilSpatialStructureElement\". In detail, \"IfcTrackFastening\", \"IfcTrackBallast\", \"IfcTrackSleeper\", \"IfcTrackTurnout\", and \"IfcTrackRail\" were represented as physical entities, indicating fasteners, ballasts, sleepers, turnouts, and rails, respectively. Regarding the attributes of the extended physical entities, \"PredefinedType\", which is an attribute to represent materials, and \"FunctionType\", which is an attribute to represent shapes, were added. Figure 4: Extended IFC entities for railway tracks: (**a**) Extension of physical entities; (**b**) extension of spatial entities. The spatial entities were extended to \"IfcTrack\", which represents the entire section, and \"IfcTrackPart\", which represents parts of the section. Representation of the usage purpose, track gauge, and slack from the railway track design parameters as single physical entities is not suitable; therefore, \"PredefinedType\", \"TrackGauge\", and \"Slack\" were added as attributes in \"IfcTrackPart\", which contains spatial information. Moreover, an enumeration on the type was added for each entity. Table 1 lists the attributes and types of added entities in Figure 4. For example, \"IfcTrackBallastTypeEnum\" is added to \"IfcTrackBallast\" so that \"CRUSHEDSTONEBallLAST\", \"PEBBLEBALLAST\", \"SANDBALLAST\", \"SLAGBALLAST\", \"CONBALLAST\", \"USERDEFINED\", and \"NOTDEFINED\" can be specified. The alignment elements added in IFCA \(\times\) 2 were used for alignment information. These alignment elements represent alignment through \"IFCAlignment\" and contain \"IFCAlignmentCurve\" as their internal attribute. \"IFCAlignmentCurve\" is an entity for representing 3D curves and includes the horizontal alignment \"IFCAlignment2 DHorizontal\" and vertical alignment \"IFCAlignment2 DVertical\" as its attributes. In this study, the connections between spatial entities in the same hierarchy were represented through \"IfcRelAggregates\", and the connections between the spatial and physical entities included as spatial entities were represented through \"IfcRelContainedInSpatialStructure\". The connections between the spatial or physical entities and the attributes of these entities were represented through \"IfcRelDefinesByProperties\".