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 1.
There are several scenarios to define the same property set on the object type definition and object occurrence side:
Figure 1 — Type definition relationships
The following table provides an example of assigning
|properties assigned to IfcWall||properties assigned to IfcWallType||resulting property value for individual wall|
|- ExtendToStructure = TRUE||TRUE|
|- ThermalTransmittance = 0.375||0.375|
|- ExtendToStructure = FALSE||- ExtendToStructure = TRUE||FALSE|
HISTORY New entity in IFC2x.
|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, |
> NOTE only the last modification in stored - either as addition, deletion or modification.
> IFC4 CHANGE The attribute has been changed to be OPTIONAL.
|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.|
|5||RelatedObjects||SET [1:?] OF IfcObject|
|6||RelatingType||IfcTypeObject||Reference to the type (or style) information for that object or set of objects.|
IfcRoot assigns the globally unique ID. In addition it may provide for a name and a description about the concept.
Ownership, history, and merge state is captured using IfcOwnerHistory.
ENTITY IfcRelDefinesByType SUBTYPE OF (IfcRelDefines); RelatedObjects : SET [1:?] OF IfcObject; RelatingType : IfcTypeObject; END_ENTITY;