Below is a sequence diagram for making a flght reservation by a customer.
The actor initiating the sequence of message is a customer who is planning
a trip.
The customer sends a makeReservation() message to a travel agency, which issues
a self call to determine which airline flight is possible to be booked, sends
a isFlightAvailable() message to a air company. It ask the air company if the
flight is available. If so, the air company makes a Reservation.
Each vertical line represents the time that an object exists. Each arrow is
a message call. An arrow goes from the sender of the activation bar of the message
on the receiver's lifeline. The activation bar represents the duration of execution
of the message.
