I agree that “traversing the tag tree” should narrow the search results.
The issue here - as far as I see it - is what happen when you perform a query on a “head tag” for 2 images that share the same tags, with the same hierarchy, but have been tagged in a different sequence…
I’ve just tried it in digiKam, in the same sequence described in the example, and the 2 images were tagged identically and could be retrieved with the same “query” (either by searching with Nature alone or with Nature|Flower (I can’t check with Shotwell, as I’m on a Windows machine right now and don’t have time to setup a VM)
In the case of darktable, currently, double-cliking (without shift/control) on Nature would retrieve Image 1, but not Image 2, while double-clicking on Nature|Flower would retrieve both images.
I’m not sure I understand your Lightroom example, but could you confirm that if you were following the same sequence than in my example, both images would be - or not - tagged identically and could be - or not- retrieved the same way?
That said, I totally understand that darktable could implement something different than other DAM software… it’s just that - it may be just me! - I find that currently, the result is not really coherent/intuitive for users.
Thanks for listening!