Some of the shared apartments/rooms are empty during the summer. The empty shared apartments will be cleaned by cleaning company during the summer. So if you are living in an apartment where the other room is empty the cleaners might visit the apartment some day during the summer. You don’t need to do anything special to prepare their visit. If you are not home the cleaners will leave a note that they’ve been in the apartment. The cleaners will not clean the rooms where someone is living.
Cleaning the empty rooms/apartments doesn’t mean that the tenants still living in the apartments could free themselves from the duty of taking care of the apartment. If there are neglections in cleaning the tenant will receive a notice about it.
It is also possible that your flat mate changes during the summer. If you are away during the summer, it is recommended that you take your own things from the shared areas in your own room. You can also leave a welcome letter to your new flat mate attached to your room door. You can print the letter here or get it from DAS customer service.