The association relationship IfcRelAssociates refers to sources of information (most notably a classification, library, document, approval, constraint, or material). The information associated may reside internally or externally of the project data. There is no dependency implied by the association. 

• EXAMPLE: Further external information may be provided to the tank equipment (as subtype of IfcProduct)

in terms of its classification and instruction documents, the source of the additional information is held external to the project data model. 

Association relationships can be established to objects (occurrences as subtypes of IfcObject) or to types (as subtypes of IfcTypeObject). Some associations (such as approval, or document) may also be applied to property templates (as subtypes of IfcPropertyDefinition). The association relationship establishes an association between one to many objects or property templates and the associated information. The subtypes of IfcRelAssociates establish the particular semantic meaning of the association relationship.

• EXAMPLE: The classification information for the storage tank equipment may be associated to the IfcTankType (subtype of IfcTypeObject), defining the specific information for all occurrences of that tank in the project. Therefore the association of the Uniclass notation 'L6814' may be associated by a subtype of IfcRelAssociates to the type information.
• EXAMPLE: The classification information for a particular space within a building may be associated to the IfcSpace object (subtype of IfcObject), defining a particular occurrence of space. Therefore the association of the DIN notation 'NF 1.5' may be associated by a subtype of IfcRelAssociates to the object.

changes 

• IFC4 changes:
  • Entity has been changed into an ABSTRACT supertype.
  • Type of the RelatedObjects attribute changed from "set[1:?] of IfcRoot" to "set[1:?] of IfcDefinitionSelect".