need help in Web service usage scenario:Travel reservation

Hello All,
you told us in the "Web service usage scenario: Travel reservation"
http://www.w3.org/2002/04/17-ws-usecase

that The travel agent service finds a list of airlines.
please, can u tell me what is the difference between one airline & another?
(i.e. what are the advantages of each airline?)
-- 
Eman Hossny,
Teacher Assistant,
Computer Science Department,
Faculty of Computers and Information
Cairo University, Egypt

يارب العتق من النار لى ولوالديا