IFC (IFC4X3_ADD2) under development IfcRelDefinesByType

AbRV ⓘ
RV ⓘ Semantic definition

The objectified relationship IfcRelDefinesByType defines the relationship between an object type and object occurrences. The IfcRelDefinesByType is a 1-to-N relationship, as it allows for the assignment of one type information to a single or to many objects. Those objects then share the same object type, and the property sets and properties assigned to the object type.

The IfcRelDefinesByType links the object type definition with the object occurrence. Both may define properties by assigning an IfcPropertySet, including one or many subtypes of IfcProperty to either the object type or object occurrence, as shown in Figure

There are several scenarios to define the same property set on the object type definition and object occurrence side:

  1. All properties for all object occurrences of a common object type have the same value - then only the object type definition has a property set assigned.
  2. All properties for all object occurrences are different, that is there are no common property values for the object type definition - then each of the object occurrences has a property set assigned.
  3. Some properties within the same property set have common values and are assigned to the object type definition and some are occurrence specific and assigned (with potentially different values) to the object occurrences - then:
    • The sum of all properties within a given property set applicable to an object occurrence is the union of properties assigned to the object type definition plus the properties assigned to the object occurrence.
    • If the object occurrence has a property with the same IfcProperty.Name in an IfcPropertySet, as the corresponding object type definition, then the occurrence property value overrides the type property value.
instance diagram
Figure — Type definition relationships

The following table provides an example of assigning properties that can be overridden.

Properties assigned to IfcWallType Property assigned to IfcWall Resulting property value for individual wall
- ExtendToStructure = TRUE ExtendToStructure = TRUE
ThermalTransmittance = 0.375 - ThermalTransmittance = 0.375
ExtendToStructure = TRUE ExtendToStructure = FALSE ExtendToStructure = FALSE
Table 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.

Click to show 4 hidden inherited attributes Click to hide 4 inherited attributes
IfcRelDefinesByType (2)
5 RelatedObjects SET [1:?] OF IfcObject

No description available.

6 RelatingType IfcTypeObject

Reference to the type (or style) information for that object or set of objects.

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.

Click to show 2 hidden inherited concepts Click to hide 2 inherited concepts
Table Examples Formal representation

ENTITY IfcRelDefinesByType
 SUBTYPE OF (IfcRelDefines);
	RelatedObjects : SET [1:?] OF IfcObject;
	RelatingType : IfcTypeObject;
END_ENTITY; References

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Is this page difficult to understand? Let us know! Changelog IFC4

  • attribute, RelatedObjects