buildingSMART does not (and rightly so) dictate exactly what values are allowed in the
IfcClassification entity. However, this becomes a problem when BIM authors export IFCs which mean the same thing (most of us use a handful of very well known classification systems) but have different values. Similar to the work done in standardising on EPSG codes for georeferencing, I propose that a reference table be published for well known classification systems.
The OSArch community has got one here, and these are shipped with the BlenderBIM Add-on:
I invite others to critique and let me know their conventions (as well as add other classification systems).