Nextcloud and existing Samba-Shares


I am beginner in using Nextcloud. I have not even installed it yet (on my live system).
At the moment I am running a local NAS (Ubuntu 17.04 with Samba4, Apache…) that provides 5 shared folders to my clients. Let’s name them


I’d like to use NextCloud as a “frontend” to these folders. So, after the installation of NextCloud it should be possible to access all of these foldern via the web frontend and any other “NextCloud apps” (Android, Windows…)

I found a lot of tutorials that build a database from scratch with a dedicated “NextCloud data folder” to where all the data is copied to. But this is not what I want. The data MUST remain at its local directory (/mnt/data/pictures…) and NextCloud should simply index it to its database.