I am modelling a DVD Rental Store:

1. A Client gives its clientNumber to the System.
2. The System checks whenever the given clientNumber is valid.
3. The Client gives the name of the DVD he wants to rent.
4. ... n. ...I will later have to form an association between a new instance of "RentDVD" class concept to the current Client c.

My Domain Model is something like:

I've made the Contract for the first and second operations as: Preconditions: none Postconditions: there exists a Client c such that c.clientNumber = clientNumber.

Now, I don't know if I should form an association between this Client c and the DVDStore(that I intend to use as front-end). If I don't make the association, how will I later be able to "reference" this same Client? Should I be making an association between Client and a different concept?

Thanks