Property and Quantity Sets as Attributes
FME automatically converts IFC property sets and quantity sets into attributes on elements, named using the pattern SetName.PropertyName or SetName.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.