8.3.3.4 IfcReference
8.3.3.4.1 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.
8.3.3.4.2 Entity inheritance
8.3.3.4.3 Attributes
# | Attribute | Type | Description |
---|---|---|---|
IfcReference (5) | |||
1 | TypeIdentifier | 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. |
2 | AttributeIdentifier | OPTIONAL 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. |
3 | InstanceName | 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. |
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. |
5 | InnerReference | 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. |
8.3.3.4.4 Formal representation
ENTITY IfcReference;
TypeIdentifier : OPTIONAL IfcIdentifier;
AttributeIdentifier : OPTIONAL IfcIdentifier;
InstanceName : OPTIONAL IfcLabel;
ListPositions : OPTIONAL LIST [1:?] OF IfcInteger;
InnerReference : OPTIONAL IfcReference;
END_ENTITY;