IfcObjectDefinition

Semantic definitions at the entity

Entity definition

An IfcObjectDefinition is the generalization of any semantically treated thing or process, either being a type or an occurrences. Object defintions can be named, using the inherited Name attribute, which should be a user recognizable label for the object occurrance. Further explanations to the object can be given using the inherited Description attribute. A context is a specific kind of object definition as it provides the project or library context in which object types and object occurrences are defined.

Objects are independent pieces of information that might contain or reference other pieces of information. There are four essential kinds of relationships in which object definitons (by their instantiable subtypes) can be involved:

Assignment of other objects - an assignment relationship (IfcRelAssigns) that refers to other types of objects and creates a bi-directional association. The semantic of the assignment is established at the level of the subtypes of the general IfcRelAssigns relationship. There is no dependency implied a priori by the assignment.
Association to external resources - an association relationship (IfcRelAssociates) that refers to external sources of information (most notably a classification or document) and creates a uni-directional association. There is no dependency implied by the association.
Aggregation of other objects - an aggregation relationship (IfcRelAggregates) that establishes an unordered, spatial whole/part relation and creates a bi-directional relation. There is an implied dependency established.
Nesting of other objects - a nesting relationship (IfcRelNests) that establishes an ordered, non-spatial whole/part relation and creates a bi-directional relation. There is an implied dependency established.
Declaration within a context - a relationship (IfcRelDeclares) of the uppermost object definition within the object definition tree (e.g. the summary object within an object nesting tree) to the context (a project or project library). It applies the units, representation context and other context information to this object definition and all dependent ones.

NOTE The link between the uppermost object in the spatial structure tree, that is IfcSite or ifcBuilding, and the context provided by IfcProject is created using the IfcRelAggregates relationship. See IfcProject for more information.

HISTORY New abstract entity in IFC2x3.

IFC4 CHANGE The new subtype IfcContext and the relationship to context HasContext has been added . The decomposition relationship is split into ordered nesting (Nests, IsNestedBy) and un-ordered aggregating (Decomposes, IsDecomposedBy).

Attribute definitions

Attribute	Type	Cardinality	Description	G
HasAssignments	IfcRelAssigns @RelatedObjects	S[0:?]	Reference to the relationship objects, that assign (by an association relationship) other subtypes of IfcObject to this object instance. Examples are the association to products, processes, controls, resources or groups.	X
Nests	IfcRelNests @RelatedObjects	S[0:1]	References to the decomposition relationship being a nesting. It determines that this object definition is a part within an ordered whole/part decomposition relationship. An object occurrence or type can only be part of a single decomposition (to allow hierarchical strutures only). IFC4 CHANGE The inverse attribute datatype has been added and separated from Decomposes defined at IfcObjectDefinition.	X
IsNestedBy	IfcRelNests @RelatingObject	S[0:?]	References to the decomposition relationship being a nesting. It determines that this object definition is the whole within an ordered whole/part decomposition relationship. An object or object type can be nested by several other objects (occurrences or types). IFC4 CHANGE The inverse attribute datatype has been added and separated from IsDecomposedBy defined at IfcObjectDefinition.	X
HasContext	IfcRelDeclares @RelatedDefinitions	S[0:1]	References to the context providing context information such as project unit or representation context. It should only be asserted for the uppermost non-spatial object. IFC4 CHANGE The inverse attribute datatype has been added.	X
IsDecomposedBy	IfcRelAggregates @RelatingObject	S[0:?]	References to the decomposition relationship being an aggregation. It determines that this object definition is whole within an unordered whole/part decomposition relationship. An object definitions can be aggregated by several other objects (occurrences or parts). IFC4 CHANGE The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.	X
Decomposes	IfcRelAggregates @RelatedObjects	S[0:1]	References to the decomposition relationship being an aggregation. It determines that this object definition is a part within an unordered whole/part decomposition relationship. An object definitions can only be part of a single decomposition (to allow hierarchical strutures only). IFC4 CHANGE The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.	X
HasAssociations	IfcRelAssociates @RelatedObjects	S[0:?]	Reference to the relationship objects, that associates external references or other resource definitions to the object.. Examples are the association to library, documentation or classification.	X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	G
IfcRoot
1	GlobalId	IfcGloballyUniqueId		Assignment of a globally unique identifier within the entire software world.	X
2	OwnerHistory	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.	X
3	Name	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.	X
4	Description	IfcText	?	Optional description, provided for exchanging informative comments.	X
IfcObjectDefinition
	HasAssignments	IfcRelAssigns @RelatedObjects	S[0:?]	Reference to the relationship objects, that assign (by an association relationship) other subtypes of IfcObject to this object instance. Examples are the association to products, processes, controls, resources or groups.	X
	Nests	IfcRelNests @RelatedObjects	S[0:1]	References to the decomposition relationship being a nesting. It determines that this object definition is a part within an ordered whole/part decomposition relationship. An object occurrence or type can only be part of a single decomposition (to allow hierarchical strutures only). IFC4 CHANGE The inverse attribute datatype has been added and separated from Decomposes defined at IfcObjectDefinition.	X
	IsNestedBy	IfcRelNests @RelatingObject	S[0:?]	References to the decomposition relationship being a nesting. It determines that this object definition is the whole within an ordered whole/part decomposition relationship. An object or object type can be nested by several other objects (occurrences or types). IFC4 CHANGE The inverse attribute datatype has been added and separated from IsDecomposedBy defined at IfcObjectDefinition.	X
	HasContext	IfcRelDeclares @RelatedDefinitions	S[0:1]	References to the context providing context information such as project unit or representation context. It should only be asserted for the uppermost non-spatial object. IFC4 CHANGE The inverse attribute datatype has been added.	X
	IsDecomposedBy	IfcRelAggregates @RelatingObject	S[0:?]	References to the decomposition relationship being an aggregation. It determines that this object definition is whole within an unordered whole/part decomposition relationship. An object definitions can be aggregated by several other objects (occurrences or parts). IFC4 CHANGE The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.	X
	Decomposes	IfcRelAggregates @RelatedObjects	S[0:1]	References to the decomposition relationship being an aggregation. It determines that this object definition is a part within an unordered whole/part decomposition relationship. An object definitions can only be part of a single decomposition (to allow hierarchical strutures only). IFC4 CHANGE The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.	X
	HasAssociations	IfcRelAssociates @RelatedObjects	S[0:?]	Reference to the relationship objects, that associates external references or other resource definitions to the object.. Examples are the association to library, documentation or classification.	X

Definitions applying to General Usage

Instance diagram

Concept usage

Classification Association

The Classification Association concept applies to this entity.

Any object occurrence or object type can have a reference to a specific classification reference, i.e. to a particular facet within a classification system.

mvdXML Specification


<?xml version="1.0" encoding="utf-8"?>

<ConceptRoot xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" uuid="f26454ea-55a9-4d8f-a2a0-ab8a5561112d" name="IfcObjectDefinition" applicableRootEntity="IfcObjectDefinition">

 <Applicability>

  <Template ref="95f14c0b-d81c-49cb-be71-edd4e4eb395c" />

  <TemplateRules operator="and">

  </TemplateRules>

 </Applicability>

 <Concepts>

  <Concept uuid="dcfad64e-cedb-4766-b609-cfe82ae3ae44" name="Classification Association">

   <Template ref="4a224609-6578-4c75-afcf-8affa86e5ef2" />

  </Concept>

 </Concepts>

</ConceptRoot>

Concept inheritance

#	Concept	Template	Model View
IfcRoot
	Identity	Software Identity	General Usage
	Revision Control	Revision Control	General Usage
IfcObjectDefinition
	Classification Association	Classification Association	General Usage

Formal representations

XML Specification

 <xs:element name="IfcObjectDefinition" type="ifc:IfcObjectDefinition" abstract="true" substitutionGroup="ifc:IfcRoot" nillable="true"/>

 <xs:complexType name="IfcObjectDefinition" abstract="true">

  <xs:complexContent>

   <xs:extension base="ifc:IfcRoot">

    <xs:sequence>

     <xs:element name="IsNestedBy" nillable="true" minOccurs="0">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcRelNests" minOccurs="0" maxOccurs="unbounded"/>

       </xs:sequence>

       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcRelNests"/>

       <xs:attribute ref="ifc:cType" fixed="set"/>

       <xs:attribute ref="ifc:arraySize" use="optional"/>

      </xs:complexType>

     </xs:element>

     <xs:element name="IsDecomposedBy" nillable="true" minOccurs="0">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcRelAggregates" minOccurs="0" maxOccurs="unbounded"/>

       </xs:sequence>

       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcRelAggregates"/>

       <xs:attribute ref="ifc:cType" fixed="set"/>

       <xs:attribute ref="ifc:arraySize" use="optional"/>

      </xs:complexType>

     </xs:element>

    </xs:sequence>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcObjectDefinition

 ABSTRACT SUPERTYPE OF(ONEOF(IfcContext, IfcObject, IfcTypeObject))

 SUBTYPE OF (IfcRoot);

 INVERSE

  HasAssignments : SET [0:?] OF IfcRelAssigns FOR RelatedObjects;

  Nests : SET [0:1] OF IfcRelNests FOR RelatedObjects;

  IsNestedBy : SET [0:?] OF IfcRelNests FOR RelatingObject;

  HasContext : SET [0:1] OF IfcRelDeclares FOR RelatedDefinitions;

  IsDecomposedBy : SET [0:?] OF IfcRelAggregates FOR RelatingObject;

  Decomposes : SET [0:1] OF IfcRelAggregates FOR RelatedObjects;

  HasAssociations : SET [0:?] OF IfcRelAssociates FOR RelatedObjects;

END_ENTITY;

 EXPRESS-G diagram

	Objektdefinition
	Object Definition
	Définition d'objet