Communication diagram can help us to identify potential objects and operations for the ticket selling system at a later stage of development. Its collaboration shows the interaction among internal objects in the application to reserve tickets. The request arrives from the ticket selling system and is used to ﬁnd the database for the particular performance from the set of all performances. The pointer db that is returned to the ticketSeller object represents a local transient link to a performance database that is maintained during the interaction and then discarded. The ticket seller requests a number of seats to the performance; a selection of seats in various price ranges is found, temporarily locked, and returned to the kiosk for the customer’s selection. When the customer makes a selection from the list of seats, the selected seats are claimed and the rest are unlocked.