Teil zu Ganzes Beziehung ungeordnet - Relation

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.

EXAMPLE  A roof is the aggregation of the roof elements, such as roof slabs, rafters, purlins, etc. Within the same representation identifier (such as the body geometric representation), the shape representation of the roof is given by the shape representation of its 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.

HISTORY  New entity in IFC2x.
IFC4 CHANGE The attributes RelatingObject and RelatedObjects are demoted from the supertype IfcRelDecomposes.

XSD Specification:

 <xs:element name="IfcRelAggregates" type="ifc:IfcRelAggregates" substitutionGroup="ifc:IfcRelDecomposes" nillable="true"/>
 <xs:complexType name="IfcRelAggregates">
   <xs:extension base="ifc:IfcRelDecomposes">
     <xs:element name="RelatingObject" type="ifc:IfcObjectDefinition" nillable="true"/>
     <xs:element name="RelatedObjects">
        <xs:element ref="ifc:IfcObjectDefinition" maxOccurs="unbounded"/>
       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcObjectDefinition"/>
       <xs:attribute ref="ifc:cType" fixed="set"/>
       <xs:attribute ref="ifc:arraySize" use="optional"/>

EXPRESS Specification:

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

Link to EXPRESS-G diagram EXPRESS-G diagram

Attribute Definitions:

RelatingObject : The object definition, either an object type or an object occurrence, that represents the aggregation. It is the whole within the whole/part relationship.
IFC4 CHANGE  The attribute has been demoted from the supertype IfcRelDecomposes and defines the non-ordered aggregation relationship.
RelatedObjects : The object definitions, either object occurrences or object types, that are being aggregated. They are defined as the parts in the whole/part relationship. No order is implied between the parts.
IFC4 CHANGE  The attribute has been demoted from the supertype IfcRelDecomposes and defines the non-ordered set of parts within the aggregation.

Formal Propositions:

NoSelfReference : The instance to with the relation points as provided by RelatingObject shall not be contained in the set of RelatedObjects.

Inheritance Graph:

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

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