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。通过此系统可以实现如下功能：录入功能：查询功能：订票功能(Air passenger booking system: air passenger booking business activities include: query routes, ticket booking and refund processing. Through this system can achieve the following functions: Input function: Query function: Booking function)