Definition from IAI: An IfcClassificationItemRelationship is a relationship class that enables the hierarchical structure of a classification system to be exposed through its ability to contain related classification items and to be contained by a relating classification item.
HISTORY: New entity in IFC Release 2x.
ISSUES: See issue and change log for changes made in IFC Release 2x.
Use Definitions
IfcClassificationItem's can be progressively decomposed using the IfcClassificationItemRelationship such that the relationship always captures the information about the parent level (relating) item and the child level (related) items of which there can be many. The following example shows how this could be achieved for the Uniclass system.
The inverse relationships from IfcClassificationItem to IfcClassificationRelationship enable information about the relationship to be recovered by the items concerned so that they are also aware of the decomposition. The cardinality of the inverse relationship is that an IfcClassificationItem can be the classifying item in only one relationship and can be a classified item in only one relationship. This implies that there is no overlap of IfcClassificationItems. This reflects typical classification approaches which use strict hierarchical decomposition (or taxonomy) and do not have matrix relationships.
In terms of EXPRESS, this can be seen from:
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#200 IFCCLASSIFICATIONITEM (#100,#2,'Door Panel');
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#201 IFCCLASSIFICATIONITEM (#101,#2,'Door Panel');
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#202 IFCCLASSIFICATIONITEM (#102,#2,'Door Panel');
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#203 IFCCLASSIFICATIONITEM (#103,#2,'Door Panel');
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#204 IFCCLASSIFICATIONITEM (#104,#2,'Door');
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#205 IFCCLASSIFICATIONITEMRELATIONSHIP (#204,(#200,#201,#202,#203));