Metadata writing of hierarchical tags

After looking a bit closer to what is written in xmp files, it appears 
that the Xmp.dc.subject stores hierarchical tags as a flat list in 
theses files.

In fact my initial question was more on the way Digikam displays these 
tags under each image : it doesn't display a flat list (for example for 
reverse geotagging : country, State, City…) but it displays each tag and 
subtag with parent tags (i.e : country, country/state, 
country/state/city and so on).

Is there any way to display only the last tag of the hierarchy with all 
parent tags ?

Regards,

Pierre