航空客运定票的业务活动包括：查询航线、客票预定和办理退票等。试设计一个航空客运定票系统，以使上述业务可以借助计算机来完成。-Air passenger tickets business activities include: Inquiry routes, ticket booking and refund the like. Try to design a passenger ticket system, so that these businesses can make use of a computer to complete.