# IfcClassificationReference

An _IfcClassificationReference_ is a reference into a classification system or source (see _IfcClassification_) for a specific classification key (or notation).
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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 referred 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.

{ .change-ifc2x4}
> IFC4 CHANGE The attribute _Description_ and inverse attribute _HasReferences_ are added. The attribute _Identification_ has been renamed from ItemReference.

## Attributes

### ReferencedSource
The classification system or source that is referenced.
{ .change-ifc2x4}
> IFC4 CHANGE Data type changed to _IfcClassificationReferenceSelect_.

### Description
Description of the classification reference for informational purposes.
{ .change-ifc2x4}
> 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).
{ .change-ifc2x4}
> IFC4 CHANGE New attribute added at the end of the attribute list.

### ClassificationRefForObjects
The classification reference with which objects are associated.
{ .change-ifc2x4}
> 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.
{ .change-ifc2x4}
> IFC4 CHANGE New inverse attribute.