航空客运订票系统,航空客运订票的业务活动包括：查询航线、客票预定和办理退票等。试设计一个航空客运订票系统，以使上述业务可以借助计算机来完成-Air passenger booking system, air passenger ticketing business activities include: check routes, such as ticket booking and obtain refunds. Try to design a air passenger booking system, so the business can be done using computer