The IfcBuildingElementProxy is a proxy definition that provides the same functionality as subtypes of IfcBuildingElement, but without having a predefined meaning of the special type of building element, it represents. Proxies can also be used as spatial place holders or provisions, that are later replaced by special types of elements. 

One use of the proxy object is a provision for voids, i.e. where a particular volume of space is requested by an engineering function that might later be accepted or rejected. If accepted it is transformed into a void within a building element, like a wall opening, or a slab opening. The provision for voids is exchanged as an IfcBuildingElementProxy with the PredefinedType = ProvisionForVoid. Such proxy has a swept solid geometry, where the profile of the swept solid lies on/near the surface of the referred building element and the extrusion depths is equal to or bigger then (in case of round or otherwise irregular element shape) the thickness of the building element. The appropriate property set should be attached. 

In addition to the provision for voids, the building element proxy can also represent a provision for space, often the necessary space allocation for mechanical equipment that will be determined in a later design phase. The provision for space is exchanged as an IfcBuildingElementProxy with the PredefinedType = ProvisionForSpace. 

Other usages of IfcBuildingElementProxy include:

• The IfcBuildingElementProxy can be used to exchange special types of building elements for which the current specification does not yet provide a semantic definition
• The IfcBuildingElementProxy can also be used to represent building elements for which the participating applications can not provide a semantic definition

The IfcBuildingElementProxyType can be used to share common information among many occurrences of the same proxy without establishing a particular semantic meaning of the type. If no IfcBuildingElementProxyType is attached (i.e. if only occurrence information is available) the PredefinedType should be provided. If set to .USERDEFINED. a user defined value has to be provided by the ObjectType attribute. This concept can be applied to the following resources:

• IfcBuildingElementProxyType

This concept can be applied to the following resources:

• Pset_ConcreteElementGeneral
• Pset_PrecastConcreteElementFabrication
• Pset_PrecastConcreteElementGeneral
• Pset_BuildingElementProxyCommon
• Pset_ProvisionForVoid (only applies to PROVISIONFORVOID)

This concept can be applied to the following resources:

• Qto_BuildingElementProxyQuantities

The IfcBuildingElementProxy, as any subtype of IfcBuildingElement, can participate alternatively in one of the two different containment relationships:

• the Spatial Containment (defined here)
• the Element Composition

changes 

• IFC4 changes:
  • Name of the CompositionType attribute changed to PredefinedType
  • Type of the CompositionType attribute changed from "IfcElementCompositionEnum" to "IfcBuildingElementProxyTypeEnum"