Tutorials : UML modeling for information system architecture : Module 3: Create class diagrams : Lesson 3.4: Add associations between other classes
  
Lesson 3.4: Add associations between other classes
Add association lines to other classes in the diagram.
As you also modeled in the Sequence diagram, Reception uses Diary to gain information for the customer who wants to make a reservation. The association is a one-to-one relationship: There is one Reception class that deals with one Diary class.
In addition, each Customer makes one-or-more Reservations.
To model these associations
1 Draw an association line from Reception to Diary, and name it uses.
2 Draw an association line from Customer to Reservation, and name it makes.
3 Get out of drawing mode by pressing your Esc key or choosing the Select Mode pointer in the toolbox.
4 Open the definition of the uses association between Reception and Diary and set the multiplicity to Only One for the Reception class, and Only One for the Diary class.
5 Open the definition of the makes association between Customer and Reservation and set the multiplicity to Only One for Customer, and One or Many for Reservation.