The thesis makes sequence diagrams of five use cases , the five use cases are " receive mail " , " send mail " , " delete mail " , " add contact " and " delete contact " 本文郵件系統(tǒng)建立了“接收郵件” 、 “發(fā)送郵件” 、 “刪除郵件” 、 “添加聯(lián)系人”和“刪除聯(lián)系人”五個(gè)用例的順序圖。