Also we make full considering of how to abstract reusable classes and packages and arrange the algorithm logic and interface into different layers . so we can make sure the software has good reusability and translatabiliry . fifthly , we further described the process of how to analyze and design the application layer of flight information subsystem 在分析設計過程中,充分考慮到了對可重用的類和包的提取,同時采用分層設計的方法,使核心算法邏輯與外部接口處于不同的層次中,保證了軟件的可重用性和可移植性。