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
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