电子生词本 系统实现目标： 记录单词 记录文章（作为单词的上下文，可以分析出单词） 系统分为三层结构：磁盘存储、内存管理、用户交互-electronic wordlists of the system to achieve the target : a record recorded word article (as a word in the context, can analyze words) system is divided into three-tier struct