After analysis of inherit, logical and aggregation relationships among the objects, the object sets of problem domain, system data structure and application frameworks were designed, and the system extensibility was also discussed.

• 通过对象之间继承关系、逻辑关系和聚合关系的分析，设计了领域问题对象集、系统数据结构和应用框架，并讨论了系统的可扩充性。