IfcExternalReference

BACnet MVD

#### 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

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---

1

Location

IfcURIReference

?

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

X

2

Identification

IfcIdentifier

?

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

X

3 | Name | IfcLabel | ? | 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 | X

ExternalReferenceForResources

IfcExternalReferenceRelationship
@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

Rule | Description
--- | ---
WR1 | One of the attributes of IfcExternalReference should have a value assigned.

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---
IfcExternalReference

1

Location

IfcURIReference

?

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

X

2

Identification

IfcIdentifier

?

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

X

3 | Name | IfcLabel | ? | 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 | X

ExternalReferenceForResources

IfcExternalReferenceRelationship
@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;

EXPRESS-G diagram

`

References: IfcExternalReferenceRelationship IfcResourceObjectSelect IfcLightDistributionDataSourceSelect IfcObjectReferenceSelect

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