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Definition from buildingSMART: The aggregation relationship IfcRelAggregates is a special type of the general composition/decomposition (or whole/part) relationship IfcRelDecomposes. The aggregation relationship can be applied to all subtypes of object.

Some further specializations of decomposition may imply additional constraints and meanings, such as the requirement of aggregates to represent physical containment. In cases of physical containment the representation (within the same representation context) of the whole can be taken from the sum of the representations of the parts.

EXAMPLE: A roof is the aggregation of the roof elements, such as roof slabs, rafters, purlins, etc. Within the same representation context, e.g. the detailed geometric representation, the shape representation of the roof is given by the shape representation of its parts

Decompositions imply a dependency, i.e. the definition of the whole depends on the definition of the parts and the parts depend on the existence of the whole. The behaviour that is implied from the dependency has to be established inside the applications.

HISTORY: New entity in IFC Release 2x.

EXPRESS specification:

ENTITY IfcRelAggregates
SUBTYPE OF ( IfcRelDecomposes);

Inheritance graph

ENTITY IfcRelAggregates;
GlobalId  :  IfcGloballyUniqueId;
OwnerHistory  :  IfcOwnerHistory;
Name  :  OPTIONAL IfcLabel;
Description  :  OPTIONAL IfcText;
ENTITY IfcRelationship;
ENTITY IfcRelDecomposes;
RelatingObject  :  IfcObjectDefinition;
RelatedObjects  :  SET [1:?] OF IfcObjectDefinition;
ENTITY IfcRelAggregates;