IfcClassificationReference

IfcClassificationReference

Definition from IAI: An IfcClassificationReference is a reference into a classification system or source (see IfcClassification). An optional inherited ItemReferenced key is also provided to allow more specific references to classification items (or tables) by type. The inherited Name attribute allows for a human interpretable designation of a classification notation (or code) - see use definition of "Leightweight Classification".

HISTORY: New entity in IFC Release 2x.

ISSUES: See issue and change log for changes made in IFC Release 2x.

Use Definitions

Lightweight Classification

The IfcClassificationReference can be used as a form of 'lightweight' classification through the 'ItemReference' attribute inherited from the abstract IfcExternalReference class. In this case, the 'ItemReference' 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.

However, it is not recommended that this lightweight method be used in cases where more than one classification system is in use or where there may be uncertainty as to the origin or meaning of the classifcation.

```
#100 IFCFLOWEQUIPMENT (.....);
```

#200 IFCCLASSIFICATIONREFERENCE ($,'L6814','Tanking',$);

#300 IFCRELASSOCIATESCLASSIFICATION ((#200),#100);

Referencing from an External Source

Classifications of an object may be referenced from an external source rather than being contained within the IFC model. This is done through the IfcClassificationReference class. Consider the Uniclass notation "L6814" which has the title "Tanking". In this case, the optional attribute 'ItemReference' uses the title 'Tanking' that would otherwise be applied to the IfcClassificationItem (if it was to be contained in the model). The location of the classification reference may be found from a classification server that is available via the Internet. In this case, it may be something like "http://www.ncl.ac.uk/classification/uniclass/tanking.htm#6814"

```
#1 IFCCALENDARDATE (31,8,1997);
```

#2 IFCCLASSIFICATION(‘RIBA’,’1’,#1,’Uniclass’)

```
#100 IFCFLOWEQUIPMENT (.....);
```

#200 IFCCLASSIFICATIONREFERENCE ('http://www.ncl.ac.uk/classification/uniclass/tanking.htm#6814','L6814',$,#2);

#300 IFCRELASSOCIATESCLASSIFICATION ((#200),#100);

Because the relation between IfcRelAssociatesClassification and classification is actually made at the IfcClassificationNotationSelect class which allows classification to be either contained or referenced, it is possible to assign both contained and referenced classifications to an object.

```
#1 IFCCALENDARDATE (31,8,1997);
```

#2 IFCCLASSIFICATION(‘RIBA’,’1’,#1,’Uniclass’)

```
#100 IFCFLOWEQUIPMENT (.....);
```

#200 IFCCLASSIFICATIONNOTATIONFACET ('L6814');

#210 IFCCLASSIFICATIONNOTATIONFACET ('B2186');

#220 IFCCLASSIFICATIONNOTATIONFACET ('Z6793');

#300 IFCCLASSIFICATIONNOTATION ((#200,#210,#220));

#400 IFCCLASSIFICATIONREFERENCE ('http://www.ncl.ac.uk/classification/uniclass/tanking.htm#6814','L6814',$,#2);

#500 IFCRELASSOCIATESCLASSIFICATION (#100,(#300,#400));

EXPRESS specification:

ENTITY IfcClassificationReference

SUBTYPE OF (

IfcExternalReference);

ReferencedSource

OPTIONAL IfcClassification;

END_ENTITY;

Attribute definitions:

ReferencedSource

The classification system or source that is referenced.

References (2):

Name

Type

Referred through

Express-G

IfcClassificationNotationSelect

Select

Select relation

Diagram 2

IfcExternalReference

Entity

Subtype

Diagram 1

Inheritance graph

ENTITY IfcClassificationReference;

ENTITY IfcExternalReference;

Location

OPTIONAL IfcLabel;

ItemReference

OPTIONAL IfcIdentifier;

Name

OPTIONAL IfcLabel;

ENTITY IfcClassificationReference;

ReferencedSource

OPTIONAL IfcClassification;

END_ENTITY;