Definition from buildingSMART: The decomposition relationship,
IfcRelDecomposes, defines the general concept of elements being composed
or decomposed. The decomposition relationship denotes a whole/part hierarchy
with the ability to navigate from the whole (the composition) to the parts and
Decompositions may be constraint by requiring both, the whole and its
parts, to be of the same type - thus establishing a nesting relationship. Or
they may require some form of physical containment, thus establishing special
types of aggregation relationships.
NOTE: There are two special names for
decomposition, which are linguistically distinguished, nesting and aggregation.
The subtypes of IfcRelDecomposes will introduce either the nesting or
aggregation convention (see IfcRelNests and
EXAMPLE: A cost element is a nest of other
cost elements. Or a structural frame is an aggregation of beams and columns.
Both are applications of decomposition relationship.
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 decomposition relationship can be applied in a recursive manner,
i.e. a decomposed element can be part in another decomposition. Cyclic
references have to be prevented at application level.
HISTORY: New entity in IFC Release 1.5,
it is a generalization of the IFC2.0 entity IfcRelNests.
||SIZEOF(QUERY(Temp <* RelatedObjects | RelatingObject :=: Temp)) = 0;
|| The object that represents the nest or aggregation.
|| The objects being nested or aggregated.
|| The instance to which the relation RelatingObject points shall not be contained in the List of RelatedObjects.