8.6.3.2 IfcClassificationReference

8.6.3.2.1 Semantic definition

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 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.

8.6.3.2.2 Entity inheritance

1. • IfcExternalReference
2. • IfcClassificationReference
   • IfcDocumentReference
   • IfcExternallyDefinedHatchStyle
   • IfcExternallyDefinedSurfaceStyle
   • IfcExternallyDefinedTextFont
   • IfcLibraryReference

8.6.3.2.3 Attributes

#	Attribute	Type	Description
IfcExternalReference (4)
1	Location	OPTIONAL 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.
2	Identification	OPTIONAL 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).
3	Name	OPTIONAL 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).
	ExternalReferenceForResources	SET [0:?] OF IfcExternalReferenceRelationship FOR RelatingReference	Reference to all associations between this external reference and objects within the IfcResourceObjectSelect that are tagged by the external reference.
Click to show 4 hidden inherited attributes Click to hide 4 inherited attributes
IfcClassificationReference (5)
4	ReferencedSource	OPTIONAL IfcClassificationReferenceSelect	The classification system or source that is referenced.
5	Description	OPTIONAL IfcText	Description of the classification reference for informational purposes.
6	Sort	OPTIONAL IfcIdentifier	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).
	ClassificationRefForObjects	SET [0:?] OF IfcRelAssociatesClassification FOR RelatingClassification	The classification reference with which objects are associated.
	HasReferences	SET [0:?] OF IfcClassificationReference FOR ReferencedSource	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.

8.6.3.2.4 Formal representation

ENTITY IfcClassificationReference
 SUBTYPE OF (IfcExternalReference);
	ReferencedSource : OPTIONAL IfcClassificationReferenceSelect;
	Description : OPTIONAL IfcText;
	Sort : OPTIONAL IfcIdentifier;
 INVERSE
	ClassificationRefForObjects : SET [0:?] OF IfcRelAssociatesClassification FOR RelatingClassification;
	HasReferences : SET [0:?] OF IfcClassificationReference FOR ReferencedSource;
END_ENTITY;

8.6.3.2.5 References

• IfcClassification
• IfcClassificationReferenceSelect
• IfcClassificationSelect
• IfcExternalReference