Projects may define classification structures, which may be used to classify objects contained within the same project, or other referencing projects (incorporating the current project as IfcProjectLibrary).
The classification information can either be provided as an external classification reference, only referring to an IfcClassification, that holds the classification name, edition and a resource location, or to an IfcClassification containing the IfcClassificationReference's as the classification notations, and thereby allowing to include the classification system structure within the exchange structure.
The following diagram shows the generic classes and relationships used when applying this concept.
In addition, concepts may have particular importance to common or standardised industry practices and scenarios. For these specific usage scenarios, the tables below shows a recommended list of general usage patterns that users may adopt.