Property and Quantity Sets as Attributes
FME automatically converts IFC property sets and quantity sets into attributes on elements, named using the pattern SetName<delimiter>PropertyName or SetName<delimiter>QuantityName (for example, BuildingInfo.BuildingPermitId). If the same property occurs multiple times, FME combines these into a list attribute.
You can also create or extend property and quantity sets simply by adding attributes with this naming convention. Optionally, you may define a corresponding PropertySet or ElementQuantity feature, linking it to the element by adding the set's name to the element's ifc_is_defined_by{}.Name attribute.