8.6.2.1 IfcClassification

An IfcClassification is used for the arrangement of objects into a class or category according to a common purpose or their possession of common characteristics. A classification in the sense of IfcClassification is taxonomy, or taxonomic scheme, arranged in a hierarchical structure. A category of objects relates to other categories in a generalization-specialization relationship. Therefore the classification items in an classification are organized in a tree structure.

HISTORY New class in IFC Release 1.5. Modified in IFC 2x.
IFC 2x4 CHANGE Attribute Edition made optional. Attributes: PublicationLocation, Description and ReferenceTokens added. Inverse attribute HasClassificationReferences added.

Classification Use Definitions

IfcClassification identifies the classification system or source from which a classification notation is derived. Each classification reference or classification item, belonging to a single classification system, shall reference a single instance of IfcClassification. Therefore, each particular classification system or source used should have only one IfcClassification instance. However, because multiple classification is allowed, there may be many IfcClassification objects used, each identifying a different classification system or source.

A classification system declared may be either formally published (e.g. Omniclass, Uniclass, Masterformat, DIN etc.) or it may be a locally defined method of classifiying information. There are two methods to define a classification system within an IFC dataset:

  1. Including the classification system structure within the dataset: Here a hierarchical tree of IfcClassificationItem's is included that defines the classification system including the relationship between the classification items. An IfcClassificationNotation is used to classify an object.
  2. Referencing the classification system by a classification key or id: Here the IfcClassificationReference is used to assigned a classification id or key to each classified object.

EXPRESS Specification

ENTITY IfcClassification
SUBTYPE OF IfcExternalInformation;
Source : OPTIONAL IfcLabel;
Edition : OPTIONAL IfcLabel;
EditionDate : OPTIONAL IfcDate;
Name : IfcLabel;
Description : OPTIONAL IfcText;
Location : OPTIONAL IfcURIReference;
ReferenceTokens : OPTIONAL LIST [1:?] OF IfcIdentifier;
INVERSE
ClassificationForObjects : SET OF IfcRelAssociatesClassification FOR RelatingClassification;
HasReferences : SET OF IfcClassificationReference FOR ReferencedSource;
END_ENTITY;

EXPRESS-G Specification

Link to EXPRESS-G diagram

Attribute Definitions

Source : Source (or publisher) for this classification.
NOTE that the source of the classification means the person or organization that was the original author or the person or organization currently acting as the publisher.
Edition : The edition or version of the classification system from which the classification notation is derived.
NOTE the version labeling system is specific to the classification system.
IFC2x4 CHANGE The attribute has been changed to be optional.
EditionDate : The date on which the edition of the classification used became valid.
NOTE The indication of edition may be sufficient to identify the classification source uniquely but the edition date is provided as an optional attribute to enable more precise identification where required.
IFC2x4 CHANGE The data type has been changed to IfcDate, the date string according to ISO8601.
Name : The name or label by which the classification used is normally known.
NOTE Examples of names include CI/SfB, Masterformat, BSAB, Uniclass, STABU, DIN276, DIN277 etc.
Description : Additional description provided for the classification.

IFC2x4 CHANGE  New attribute added at the end of the attribute list.

Location : Resource identifier or locator, provided as URI, URN or URL, of the classification.

IFC2x4 CHANGE  New attribute added at the end of the attribute list.

ReferenceTokens : The delimiter tokens that are used to mark the boundaries of individual facets (substrings) in a classification reference.

This typically applies then the IfcClassification is used in conjuction with IfcClassificationReference's. If only one ReferenceToken is provided, it applies to all boundaries of individual facets, if more than one ReferenceToken are provided, the first token applies to the first boundary, the second token to the second boundary, and the nth token to the nth and any additional boundary.
NOTE  Tokens are typically recommended within the classification itself and each token will have a particular role.
EXAMPLE 1  To indicate that the facet delimiter used for DIN277-2 reference key "2.1" ("Office rooms") is ".", a single ReferenceToken ['.'] is provided. To indicate that the facet delimiter used for Omniclass Table 13 (space by function) reference key "13-15 11 34 11" ("Office") are "-" and " ", two ReferenceToken's ['-', ' '] are provided.
EXAMPLE 2  The use of ReferenceTokens can also be extended to include masks. The use need to be agreed in view definitions or implementer agreements that stipulates a "mask syntax" that should be used.

IFC2x4 CHANGE  New attribute added at the end of the attribute list.

ClassificationForObjects : The classification with which objects are associated.
IFC2x4 CHANGE  New inverse attribute.
HasReferences : The classification references to which the classification applies. It can either be the final classification notation, or an intermediate classification item.

Inheritance Graph

ENTITY IfcClassification
ENTITY IfcExternalInformation
ENTITY IfcClassification
Source : OPTIONAL IfcLabel;
Edition : OPTIONAL IfcLabel;
EditionDate : OPTIONAL IfcDate;
Name : IfcLabel;
Description : OPTIONAL IfcText;
Location : OPTIONAL IfcURIReference;
ReferenceTokens : OPTIONAL LIST [1:?] OF IfcIdentifier;
INVERSE
ClassificationForObjects : SET OF IfcRelAssociatesClassification FOR RelatingClassification;
HasReferences : SET OF IfcClassificationReference FOR ReferencedSource;
END_ENTITY;