# 5.1.3.20 IfcRelAggregates

## 5.1.3.20.1 Semantic definition

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 IfcObjectDefinition.

In cases of aggregation of physical elements into a physical aggregate the shape representation of the whole (within the same representation identifier) can be taken from the sum of the shape representations of the parts.

Decompositions imply a dependency, implying that 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 relationship has to be established inside the applications.

## 5.1.3.20.7 Formal representation

ENTITY IfcRelAggregates
SUBTYPE OF (IfcRelDecomposes);
RelatingObject : IfcObjectDefinition;
RelatedObjects : SET [1:?] OF IfcObjectDefinition;
WHERE
NoSelfReference : SIZEOF(QUERY(Temp <* RelatedObjects | RelatingObject :=: Temp)) = 0;
END_ENTITY;

## 5.1.3.20.8 References

### 5.1.3.20.9 Changelog

#### 5.1.3.20.9.1 IFC4

• attribute, RelatedObjects
• attribute, RelatingObject
• where rule, NoSelfReference