188.8.131.52.1 Semantic definition
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.
184.108.40.206.2 Entity inheritance
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.
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.
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.
|4||ListPositions||OPTIONAL LIST [1:?] OF IfcInteger||
Optionally 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.
Optional reference to an inner value for ENTITY, SELECT, SET, or LIST attributes. A path may be formed by linking IfcReference instances together.
220.127.116.11.4 Formal representation
ENTITY IfcReference; TypeIdentifier : OPTIONAL IfcIdentifier; AttributeIdentifier : OPTIONAL IfcIdentifier; InstanceName : OPTIONAL IfcLabel; ListPositions : OPTIONAL LIST [1:?] OF IfcInteger; InnerReference : OPTIONAL IfcReference; END_ENTITY;