IfcReference

BACnet MVD

#### IfcReference

Natural language names

| Bezug
| Reference
| Référence

Change log

Item | SPF | XML | Change | Description
--- | --- | --- | --- | ---
IFC2x3 to IFC4
IfcReference |  |  | ADDED |
IFC4 Addendum 1
IfcReference |  |  |  |
ListPositions |  |  | MODIFIED | Type changed from INTEGER to IfcInteger.

##### Semantic definitions at the entity

Entity definition

This entity is used to refer to a value of an attribute on an instance. It may refer to the value of a scalar attribute or a value within a collection-based attribute. Referenced attributes may be direct values, object references, collections, inverse object references, and inverse collections. References may be chained to form a path of object-attribute references.

Attribute definitions

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

1

TypeIdentifier

IfcIdentifier

?

Optional identifier of the entity or type such as 'IfcMaterialLayerSet'. For entity, type, or select-based references within a collection, this resolves the reference to such type. If omitted, the type is assumed to be the same as the declared referencing attribute.

> EXAMPLE IfcRelAssociatesMaterial.RelatingMaterial may be resolved to IfcMaterialLayerSet.

X

2 | AttributeIdentifier | IfcIdentifier | ? | Optionally identifies a direct or inverse attribute within an entity such as 'MaterialLayers'. If TypeIdentifier is specified and refers to an entity, the attribute must exist within the referenced entity. A null value indicates a reference to the type or entity itself, such as for indicating that the type of a value must match a specified constraint. |  | X

3

InstanceName

IfcLabel

?

Optionally identifies an instance within a collection according to name. If the instance has an attribute called 'Name', such attribute is used for comparison; otherwise the first STRING-based attribute of the entity is used.

> EXAMPLE IfcRoot-based entities such as IfcPropertySet use the Name attribute; IfcRepresentation entities use the RepresentationIdentifier attribute.

X

4 | ListPositions | IfcInteger | ? L[1:?] | Optionally identifies an instance within a collection according to position starting at 1. For referencing single-level collections, this attribute contains a single member; for referencing multi-level collections, then this LIST attribute contains multiple members starting from the outer-most index. |  | X

5

InnerReference

IfcReference

?

Optional reference to an inner value for ENTITY, SELECT, SET, or LIST attributes. A path may be formed by linking IfcReference instances together.

> EXAMPLE A material layer thickness may be referenced using several instances: #1=IFCREFERENCE($,'IfcSlab','HasAssociations',#2); #2=IFCREFERENCE($,'IfcMaterialLayerSet','MaterialLayers',#3); #3=IFCREFERENCE('Core','IfcMaterialLayer','LayerThickness',$);

X

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

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

1

TypeIdentifier

IfcIdentifier

?

Optional identifier of the entity or type such as 'IfcMaterialLayerSet'. For entity, type, or select-based references within a collection, this resolves the reference to such type. If omitted, the type is assumed to be the same as the declared referencing attribute.

> EXAMPLE IfcRelAssociatesMaterial.RelatingMaterial may be resolved to IfcMaterialLayerSet.

X

2 | AttributeIdentifier | IfcIdentifier | ? | Optionally identifies a direct or inverse attribute within an entity such as 'MaterialLayers'. If TypeIdentifier is specified and refers to an entity, the attribute must exist within the referenced entity. A null value indicates a reference to the type or entity itself, such as for indicating that the type of a value must match a specified constraint. |  | X

3

InstanceName

IfcLabel

?

Optionally identifies an instance within a collection according to name. If the instance has an attribute called 'Name', such attribute is used for comparison; otherwise the first STRING-based attribute of the entity is used.

> EXAMPLE IfcRoot-based entities such as IfcPropertySet use the Name attribute; IfcRepresentation entities use the RepresentationIdentifier attribute.

X

4 | ListPositions | IfcInteger | ? L[1:?] | Optionally identifies an instance within a collection according to position starting at 1. For referencing single-level collections, this attribute contains a single member; for referencing multi-level collections, then this LIST attribute contains multiple members starting from the outer-most index. |  | X

5

InnerReference

IfcReference

?

Optional reference to an inner value for ENTITY, SELECT, SET, or LIST attributes. A path may be formed by linking IfcReference instances together.

> EXAMPLE A material layer thickness may be referenced using several instances: #1=IFCREFERENCE($,'IfcSlab','HasAssociations',#2); #2=IFCREFERENCE($,'IfcMaterialLayerSet','MaterialLayers',#3); #3=IFCREFERENCE('Core','IfcMaterialLayer','LayerThickness',$);

X

##### Formal representations

XML Specification
`<xs:element name="IfcReference" type="ifc:IfcReference" substitutionGroup="ifc:Entity" nillable="true"/>
<xs:complexType name="IfcReference">
<xs:complexContent>
<xs:extension base="ifc:Entity">
<xs:sequence>
<xs:element name="InnerReference" type="ifc:IfcReference" nillable="true" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="TypeIdentifier" type="ifc:IfcIdentifier" use="optional"/>
<xs:attribute name="AttributeIdentifier" type="ifc:IfcIdentifier" use="optional"/>
<xs:attribute name="InstanceName" type="ifc:IfcLabel" use="optional"/>
<xs:attribute name="ListPositions" use="optional">
<xs:simpleType>
<xs:restriction>
<xs:simpleType>
<xs:list itemType="ifc:IfcInteger"/>
</xs:simpleType>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:complexContent>
</xs:complexType>
`
EXPRESS Specification
`ENTITY IfcReference;
TypeIdentifier : OPTIONAL IfcIdentifier;
AttributeIdentifier : OPTIONAL IfcIdentifier;
InstanceName : OPTIONAL IfcLabel;
ListPositions : OPTIONAL LIST [1:?] OF IfcInteger;
InnerReference : OPTIONAL IfcReference;
END_ENTITY;

EXPRESS-G diagram

`

References: IfcMetric IfcReference IfcMetricValueSelect IfcAppliedValueSelect IfcTableColumn

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