IfcExternalReference

Natural language names
Externer Bezug
External Reference
Référence externe
Semantic definitions at the entity
Entity definition

An IfcExternalReference is the identification of information that is not explicitly represented in the current model or in the project database (as an implementation of the current model). Such information may be contained in classifications, documents or libraries. The IfcExternalReference identifies a particular item, such as a dictionary entry, a classification notation, or a document reference within the external source.

Only the Location (as a URL) is given to describe the place where the information can be found. Also an optional Identification as a key to allow more specific references (as to sections or tables) is provided. The Identification defines a system interpretable method to identify the relevant part of information at the source. In addition a human interpretable Name can be assigned to identify the information subject, such as a classification code.

IfcExternalReference is an abstract supertype of all external reference entities.

HISTORY  New entity in IFC2x.

IFC 2x4 CHANGE  Attribute Identification renamed from ItemReference, attribute Location datatype changed, and inverse attribute ExternalReferenceForResources added.

Attribute definitions
#AttributeTypeCardinalityDescription G
1LocationIfcURIReference? Location, where the external source (classification, document or library) can be accessed by electronic means. The electronic location is provided as an URI, and would normally be given as an URL location string.
IFC4 CHANGE  The data type has been changed from IfcLabel to IfcURIReference
.
X
2IdentificationIfcIdentifier? The Identification provides a unique identifier of the referenced item within the external source (classification, document or library). It may be provided as
  • a key, e.g. a classification notation, like NF2.3
  • a handle
  • a uuid or guid
It may be human readable (such as a key) or not (such as a handle or uuid) depending on the context of its usage (which has to be determined by local agreement).
IFC4 CHANGE Attribute renamed from ItemReference for consistency.
X
3NameIfcLabel? Optional name to further specify the reference. It can provide a human readable identifier (which does not necessarily need to have a counterpart in the internal structure of the document). X
ExternalReferenceForResourcesIfcExternalReferenceRelationship
@RelatingReference
S[0:?]Reference to all associations between this external reference and objects within the IfcResourceObjectSelect that are tagged by the external reference.
IFC4 CHANGE  New inverse attribute added with upward compatibility.
X
Formal Propositions
RuleDescription
WR1One of the attributes of IfcExternalReference should have a value assigned.
Inherited definitions from supertypes
Entity inheritance IfcClassificationReference IfcDocumentReference IfcExternallyDefinedHatchStyle IfcExternallyDefinedSurfaceStyle IfcExternallyDefinedTextFont IfcLibraryReference
Attribute inheritance
#AttributeTypeCardinalityDescriptionG
IfcExternalReference
1LocationIfcURIReference? Location, where the external source (classification, document or library) can be accessed by electronic means. The electronic location is provided as an URI, and would normally be given as an URL location string.
IFC4 CHANGE  The data type has been changed from IfcLabel to IfcURIReference
.
X
2IdentificationIfcIdentifier? The Identification provides a unique identifier of the referenced item within the external source (classification, document or library). It may be provided as
  • a key, e.g. a classification notation, like NF2.3
  • a handle
  • a uuid or guid
It may be human readable (such as a key) or not (such as a handle or uuid) depending on the context of its usage (which has to be determined by local agreement).
IFC4 CHANGE Attribute renamed from ItemReference for consistency.
X
3NameIfcLabel? Optional name to further specify the reference. It can provide a human readable identifier (which does not necessarily need to have a counterpart in the internal structure of the document). X
ExternalReferenceForResourcesIfcExternalReferenceRelationship
@RelatingReference
S[0:?]Reference to all associations between this external reference and objects within the IfcResourceObjectSelect that are tagged by the external reference.
IFC4 CHANGE  New inverse attribute added with upward compatibility.
X
Formal representations
XML Specification
 <xs:element name="IfcExternalReference" type="ifc:IfcExternalReference" abstract="true" substitutionGroup="ifc:Entity" nillable="true"/>
 <xs:complexType name="IfcExternalReference" abstract="true">
  <xs:complexContent>
   <xs:extension base="ifc:Entity">
    <xs:attribute name="Location" type="ifc:IfcURIReference" use="optional"/>
    <xs:attribute name="Identification" type="ifc:IfcIdentifier" use="optional"/>
    <xs:attribute name="Name" type="ifc:IfcLabel" use="optional"/>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>
EXPRESS Specification
ENTITY IfcExternalReference
 ABSTRACT SUPERTYPE OF(ONEOF(IfcClassificationReference, IfcDocumentReference, IfcExternallyDefinedHatchStyle, IfcExternallyDefinedSurfaceStyle, IfcExternallyDefinedTextFont, IfcLibraryReference));
  Location : OPTIONAL IfcURIReference;
  Identification : OPTIONAL IfcIdentifier;
  Name : OPTIONAL IfcLabel;
 INVERSE
  ExternalReferenceForResources : SET [0:?] OF IfcExternalReferenceRelationship FOR RelatingReference;
 WHERE
  WR1 : EXISTS(Identification) OR EXISTS(Location) OR EXISTS(Name);
END_ENTITY;

Link to EXPRESS-G diagram EXPRESS-G diagram

References  References: IfcExternalReferenceRelationship IfcResourceObjectSelect IfcLightDistributionDataSourceSelect IfcObjectReferenceSelect

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