this could be taxonomy you are speaking about, e.g. if you look at OQ demos
taxonomy is just construction material (Wood/Adobe/Stone-Masonry/Unreinforced-Brick-Masonry/Concrete) because other characteristics are unknown.
Precast Reinforced Concrete with Moment Frame, 1-3 stories year built 1990-2000 would get a taxonomy string CR+PC/LFM/HBET:1,3/YBET:1990,2000.
With that you can group buildings with similar characteristics into one taxonomy - one taxonomy will use the same fragility/vulnerability function.
If you want to use simpler strings, no problem, just the id in vulnerability needs to match the taxonomy in exposure.
(Like in the example located structural_vulnerability_model.xml <vulnerabilityFunction dist="LN" id="Wood"> will be matched with the taxonomy="Wood" in exposure_model.csv).