Which config-file stores file associations in KDE/Plasma?

With the 15.04 release of Kubuntu, I switched from Gnome (Ubuntu) to KDE/Plasma. I did a clean install, while keeping my home directory. Now, libreoffice (mostly Calc) seems to be associated with every unknown file-type. Instead of manually fixing the associations for every file I encounter, I'd rather understand what went wrong and fix it by looking at the corresponding config file that KDE/Plasma uses. Which config-file is it?