Dear all,
On an Zyxel NSA 325 v2 I had installed OwnCloud 7.0.
When I uninstalled OwnCloud, the uninstall procedure deleted the
/usr/local/apache/htdocs/adv,/pkg/ownCloud/data/admin/files,
that is the folder of the data files.
Since there is no way to retrieve data files back, I mention it as a bug.