#### 8.3.3.2 IfcClassificationReference

| Référence de classification
| Klassifikationseintrag

An IfcClassificationReference is a reference into a classification system or source (see IfcClassification) for a specific classification key (or notation).

The inherited attributes have the following meaning:

- Identification: holds the key provided for a specific references to classification items (or tables).
- Name: allows for a human interpretable designation of a classification notation.
- Location: optionally holds a direct URI link into the classification system (or source) to hyperlink the classification key.

The IfcClassificationReference can either be assigned directly to the IfcClassification, such as if no classification hierarchy has to be included, or it references the parent classification notation, if the fully classification hierarchy is included in the data set. The first is refered to as "lightweight classification", and the second as "full classification". The attribute ReferencedSource then holds the following information (choice by IfcClassificationReferenceSelect):

1. being of type IfcClassification: direct reference to the classification system (with meta information provided);
2. being of type IfcClassificationReference: reference to the parent classification notation within the classification hierarchy.

> EXAMPLE The IfcClassificationReference can be used as a form of 'lightweight' classification through the 'Identification' attribute inherited from the abstract IfcExternalReference class. In this case, the 'Identification' could take (for instance) the Uniclass notation "L6814" which, if the classification was well understood by all parties and was known to be taken from a particular classification source, would be sufficient. The Name attribute could be the title "Tanking". This would remove the need for the overhead of the more complete classification structure of the model.

> HISTORY New entity in IFC2x.

> IFC4 CHANGE The attribute Description and inverse attribute HasReferences are added. The attribute Identification has been renamed from ItemReference.

XSD Specification:

<xs:element name="IfcClassificationReference" type="ifc:IfcClassificationReference" substitutionGroup="ifc:IfcExternalReference" nillable="true"/>
<xs:complexType name="IfcClassificationReference">
<xs:complexContent>
<xs:extension base="ifc:IfcExternalReference">
<xs:sequence>
<xs:element name="ReferencedSource" nillable="true" minOccurs="0">
<xs:complexType>
<xs:group ref="ifc:IfcClassificationReferenceSelect"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>

EXPRESS Specification:

ENTITY IfcClassificationReference

| SUBTYPE OF (IfcExternalReference);

ReferencedSource | : | OPTIONAL IfcClassificationReferenceSelect;
Description | : | OPTIONAL IfcStrippedOptional;
Sort | : | OPTIONAL IfcStrippedOptional;

| INVERSE

ClassificationRefForObjects | : | SET [0:?] OF IfcRelAssociatesClassification FOR RelatingClassification;
HasReferences | : | SET [0:?] OF IfcClassificationReference FOR ReferencedSource;

END_ENTITY;

Attribute Definitions:

ReferencedSource | : | The classification system or source that is referenced. IFC4 CHANGE Data type changed to IfcClassificationReferenceSelect.
Description | : | Description of the classification reference for informational purposes. IFC4 CHANGE New attribute added at the end of the attribute list.
Sort | : | Optional identifier to sort the set of classification references within the referenced source (either a classification facet of higher level, or the classification system itself). IFC4 CHANGE New attribute added at the end of the attribute list.
ClassificationRefForObjects | : | The classification reference with which objects are associated. IFC4 CHANGE New inverse attribute.
HasReferences | : | The parent classification references to which this child classification reference applies. It can either be the final classification item leaf node, or an intermediate classification item. IFC4 CHANGE New inverse attribute.

Inheritance Graph:

ENTITY IfcClassificationReference

| ENTITY IfcExternalReference

Location | : | OPTIONAL IfcStrippedOptional;
Identification | : | OPTIONAL IfcIdentifier;
Name | : | OPTIONAL IfcStrippedOptional;

| INVERSE

| ENTITY IfcClassificationReference

ReferencedSource | : | OPTIONAL IfcClassificationReferenceSelect;
Description | : | OPTIONAL IfcStrippedOptional;
Sort | : | OPTIONAL IfcStrippedOptional;

| INVERSE

ClassificationRefForObjects | : | SET [0:?] OF IfcRelAssociatesClassification FOR RelatingClassification;
HasReferences | : | SET [0:?] OF IfcClassificationReference FOR ReferencedSource;

END_ENTITY;

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