3.2.2 System domain
The DVD Library holds DVDs of a number of films. It may have any number of copies of each film. The system should, for each film, hold the film's title; no two films have the same title.
A library member can borrow any DVD of a film that is not currently on loan. However, no member can have more than six DVDs on loan at once. A borrowed DVD must be returned within three days. When a library member returns a DVD it immediately becomes available for loan to other members.
Each DVD has a unique identifying number.
Each member of the library has a unique membership number; the system also holds each member's name.