nominal values (nominalsize / pressure class) and pipe schedule

when talking of pipingcomponents, properties like “nominal size”, “pressure class”, “pipe schedule” are often discussed. My understanding the nominal size in ifc is covered by Pset_PipeSegmentTypeCommon, and I see PressureRating on Pset_BoilerTypeCommon

our product managers claim the NominalSize is not a unit, but more of an enum or a string. my own investigation led to believe the nominalsize is always one of the pre-defined values according to ASME B36.10 or other standards.

was it something we overlooked, or was it a conscious decision to use a unit here and then why?

additionally, do we know if users ever use IfcClassificationReference to model PressureClass or PipeSize? PipeSchedule?

how is the pipe schedule modeled in IFC?

So… are you saying depending on classification system, the nominal size may be a value from different definition ranges (or value domain)?

I guess baseline IFC has no general recommendation for this case, it is very specific and maybe a subject to define at MVD or Exchange Requirement level.

Classifications are associated with items, and more than one classification system can be used same time. It sounds you want more than one NominalSize value in multi-classification case?

Maybe keeping value in physical units is more general - receiver can know classification system it wants to use and find matched enumeration value?

Have you any knowledge about target downstream application?