外观模式（Facade pattern）涉及到子系统的一些类。所谓子系统，是为提供一系列相关的特征（功能）而紧密关联的一组类。例如，一个Account类、Address类和CreditCard类相互关联，成为子系统的一部分，提供在线客户的特征。-Appearance model (Facade pattern) related to some type of subsystem. The so-called sub-system is to provide a range of related features (function) and a group of closely related categories. For example, an Account category, Address Class and Class CreditCard interrelated and become part of subsystem to provide online customer characteristics.