thank you for this 6-years old Question, because it is exactly my QUESTION of the DAY!
Is there a solution for tagging and sharing per “virtuals folders or collections” anywhere?
As far as I understand, therefore has to be a database solution implemented as an underlying layer?
And this Database overstretches the “real” filesystem?
Oh, just I found more keywords here:
“Digitile Document Tag Management versus Google Drive Labels (Tags)”
(I have to crop here the weblink - digitile resources-organize-google-drive)
But certainly, I need this for my Next/Owncloud onPremise Server without Googles services.