8.4.3.1 IfcClassification

Classification
Klassifikationssystem

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.

The IfcClassification identifies the classification system or source to which a classification reference refers to. Each classification reference may reference an instance of IfcClassification. A classification system declared may be either formally published, or it may be a locally defined method of classifiying information.

NOTE  Examples for such formally published classifications are Omniclass, Uniclass, Masterformat, or DIN277.

There are two methods to define and reference a classification system:

  1. Including the classification system structure within the dataset: Here a hierarchical tree of IfcClassificationReference's is included that defines the classification system including the relationship between the classification items. The ReferencedSource attribute of IfcClassificationReference links the classification item to the parent item, and the parent item finally to the IfcClassification.
  2. Referencing the classification system by a classification key or id: Here the IfcClassificationReference is used to assign a classification id or key as Identification attribute and it may link by ReferencedSource attribute directly to the IfcClassification.
HISTORY  New entity in IFC1.5
IFC 2x4 CHANGE  Attribute Edition made optional. Attributes: Description, Location, and ReferenceTokens and inverse attribute HasReferences added.

XSD Specification:

 <xs:element name="IfcClassification" type="ifc:IfcClassification" substitutionGroup="ifc:IfcExternalInformation" nillable="true"/>
 <xs:complexType name="IfcClassification">
  <xs:complexContent>
   <xs:extension base="ifc:IfcExternalInformation">
    <xs:sequence>
     <xs:element name="ReferenceTokens" nillable="true" minOccurs="0">
      <xs:complexType>
       <xs:sequence>
        <xs:element ref="ifc:IfcIdentifier-wrapper" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcIdentifier-wrapper"/>
       <xs:attribute ref="ifc:cType" fixed="list"/>
       <xs:attribute ref="ifc:arraySize" use="optional"/>
      </xs:complexType>
     </xs:element>
    </xs:sequence>
    <xs:attribute name="Source" type="ifc:IfcLabel" use="optional"/>
    <xs:attribute name="Name" type="ifc:IfcLabel" use="optional"/>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>

EXPRESS Specification:

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

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.
IFC4 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.
IFC4 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.
IFC4 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.
IFC4 CHANGE  New attribute added at the end of the attribute list.
ClassificationForObjects : The classification with which objects are associated.
IFC4 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 IfcStrippedOptional;
EditionDate : OPTIONAL IfcStrippedOptional;
Name : IfcLabel;
Description : OPTIONAL IfcStrippedOptional;
Location : OPTIONAL IfcStrippedOptional;
ReferenceTokens : OPTIONAL LIST [1:?] OF IfcIdentifier;
INVERSE
ClassificationForObjects : SET OF IfcRelAssociatesClassification FOR RelatingClassification;
HasReferences : SET OF IfcClassificationReference FOR ReferencedSource;
END_ENTITY;

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