IFC 4.3.x development

8.3.3.4 IfcReference

Change log

IFC4

added

8.3.3.4.1 Semantic definitions at the entity

This entity is used to refer to a value of an attribute on an instance. It may refer to the value of a scalar attribute or a value within a collection-based attribute. Referenced attributes may be direct values, object references, collections, inverse object references, and inverse collections. References may be chained to form a path of object-attribute references.

8.3.3.4.1 Attributes

#Attribute Type Description
IfcReference
1TypeIdentifier OPTIONAL IfcIdentifier Optional identifier of the entity or type such as 'IfcMaterialLayerSet'. For entity, type, or select-based references within a collection, this resolves the reference to such type.

If omitted, the type is assumed to be the same as the declared referencing attribute.

> EXAMPLE  IfcRelAssociatesMaterial.RelatingMaterial may be resolved to IfcMaterialLayerSet.
2AttributeIdentifierOPTIONAL IfcIdentifier Optionally identifies a direct or inverse attribute within an entity such as 'MaterialLayers'.

If TypeIdentifier is specified and refers to an entity, the attribute must exist within the referenced entity.

A null value indicates a reference to the type or entity itself, such as for indicating that the type of a value must match a specified constraint.
3InstanceName OPTIONAL IfcLabel Optionally identifies an instance within a collection according to name. If the instance has an attribute called 'Name', such attribute is used for comparison; otherwise the first STRING-based attribute of the entity is used.

> EXAMPLE  IfcRoot-based entities such as IfcPropertySet use the Name attribute; IfcRepresentation entities use the RepresentationIdentifier attribute.
4ListPositions OPTIONAL LIST [1:?] OF IfcIntegerOptionally identifies an instance within a collection according to position starting at 1. For referencing single-level collections, this attribute contains a single member; for referencing multi-level collections, then this LIST attribute contains multiple members starting from the outer-most index.
5InnerReference OPTIONAL IfcReference Optional reference to an inner value for ENTITY, SELECT, SET, or LIST attributes.

A path may be formed by linking IfcReference instances together.

> EXAMPLE  A material layer thickness may be referenced using several instances: #1=IFCREFERENCE($,'IfcSlab','HasAssociations',#2); #2=IFCREFERENCE($,'IfcMaterialLayerSet','MaterialLayers',#3); #3=IFCREFERENCE('Core','IfcMaterialLayer','LayerThickness',$);

8.3.3.4.2 Entity inheritance

dot_inheritance IfcReference IfcReference

8.3.3.4.3 Formal representations

ENTITY IfcReference;
	TypeIdentifier : OPTIONAL IfcIdentifier;
	AttributeIdentifier : OPTIONAL IfcIdentifier;
	InstanceName : OPTIONAL IfcLabel;
	ListPositions : OPTIONAL LIST [1:?] OF IfcInteger;
	InnerReference : OPTIONAL IfcReference;
END_ENTITY;