IFC 4.3.x development

5.1.3.41 IfcRelDefinesByType

Change log

IFC4

additionsattributesRelatedObjects

5.1.3.41.1 Semantic definitions at the entity

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:

  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 occurrence 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 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
Pset_WallCommon Pset_WallCommon  
 - ExtendToStructure = TRUE   TRUE
   - ThermalTransmittance = 0.375 0.375
 - ExtendToStructure = FALSE  - ExtendToStructure = TRUE FALSE

HISTORY  New entity in IFC2x.

IFC4 CHANGE  The attribute RelatedObjects had been demoted from the supertype IfcRelDefines to IfcRelDefinesByType.

5.1.3.41.1 Attributes

#Attribute Type Description
IfcRoot
1GlobalId IfcGloballyUniqueId Assignment of a globally unique identifier within the entire software world.
2OwnerHistory OPTIONAL IfcOwnerHistoryAssignment 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.
3Name 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.
4Description OPTIONAL IfcText Optional description, provided for exchanging informative comments.
IfcRelationship
IfcRelDefines
IfcRelDefinesByType
5RelatedObjectsSET [1:?] OF IfcObject
6RelatingType IfcTypeObject Reference to the type (or style) information for that object or set of objects.

5.1.3.41.2 Entity inheritance

dot_inheritance IfcRelDefinesByType IfcRelDefinesByType IfcRelDefines IfcRelDefines IfcRelDefinesByType->IfcRelDefines IfcRelDefines_children 3 more... IfcRelDefines_children->IfcRelDefines IfcRelationship IfcRelationship IfcRelDefines->IfcRelationship IfcRelationship_children 5 more... IfcRelationship_children->IfcRelationship IfcRoot IfcRoot IfcRelationship->IfcRoot IfcObjectDefinition IfcObjectDefinition IfcObjectDefinition->IfcRoot IfcPropertyDefinition IfcPropertyDefinition IfcPropertyDefinition->IfcRoot

5.1.3.41.3 Definitions applying to General Usage

5.1.3.41.3.1 Identity

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

5.1.3.41.3.2 Revision Control

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

5.1.3.41.4 Formal representations

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