IFC (IFC4X3_ADD2) under development IfcRelDefinesByObject Semantic definition

The objectified relationship IfcRelDefinesByObject defines the relationship between an object taking part in an object type decomposition and an object occurrence taking part in an occurrence decomposition of that type.

The IfcRelDefinesByObject is a 1-to-N relationship, as it allows for the assignment of one declaring object information to a single or to many reflected objects. Those objects then share the same object property sets and, for subtypes of IfcProduct, the eventually assigned representation maps.

Only objects that take part in a type decomposition and in an occurrence decomposition of the same type can be connected by the IfcRelDefinesByObject relationship. The IfcRelDefinesByObject links the decomposed object type part, also called the "declaring part" with the occurrence of that part inside the occurrence of the decomposed type, also called the "reflected part", as shown in Figure

instance diagram
Figure — Part definition relationships

The IfcRelDefinesByObject can be used together with the shape representations of the product type as shown in Figure The IfcShapeRepresentation of the "declaring part" is referenced by the "reflected part". The IfcObjectPlacement of the model occurrence (the whole) determines the position within the project context.

geometry diagram
Figure — Part definition relationships with shape representation Entity inheritance Attributes

# Attribute Type Description
IfcRoot (4)
1 GlobalId IfcGloballyUniqueId

Assignment of a globally unique identifier within the entire software world.

2 OwnerHistory OPTIONAL IfcOwnerHistory

Assignment of the information about the current ownership of that object, including owning actor, application, local identification and information captured about the recent changes of the object,

3 Name OPTIONAL IfcLabel

Optional name for use by the participating software systems or users. For some subtypes of IfcRoot the insertion of the Name attribute may be required. This would be enforced by a where rule.

4 Description OPTIONAL IfcText

Optional description, provided for exchanging informative comments.

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IfcRelDefinesByObject (2)
5 RelatedObjects SET [1:?] OF IfcObject

Objects being part of an object occurrence decomposition, acting as the "reflecting parts" in the relationship.

6 RelatingObject IfcObject

Object being part of an object type decomposition, acting as the "declaring part" in the relationship.

Table Concept usage

Concept Usage Description
IfcRoot (2)
Revision Control General

Ownership, history, and merge state is captured using IfcOwnerHistory.

Software Identity General

IfcRoot assigns the globally unique ID. In addition it may provide for a name and a description about the concept.

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Table Formal representation

ENTITY IfcRelDefinesByObject
 SUBTYPE OF (IfcRelDefines);
	RelatedObjects : SET [1:?] OF IfcObject;
	RelatingObject : IfcObject;
END_ENTITY; References

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