如何绘制UML用例图-UML Use Case Diagram？
摘要：用例图是UML中最简单，使用最高频的图之一，它通常用于诠释“这个软件做了什么”。用例图的的表达非常简单并且通俗易懂，不论研发、产品、测试，还是完全不懂软件的外行，用例图基本都能被看懂。
.wj_nav { display: inline-block; width: 100%; margin-top: 0; margin-bottom: 0.375rem }
.wj_nav_1 { padding-left: 1rem }
.wj_nav_2 { padding-left: 2rem }
.wj_nav span { display: inline-block; margin-right: 0.375rem; color: rgba(102, 102, 102, 1) }
.wj_nav a, .wj_nav a:link, .wj_nav a:visited { color: rgba(51, 51, 51, 1); text-decoration: underline }
.wj_nav a:hover { color: rgba(255, 102, 0, 1); text-decoration: none }
.wj_title_1 { display: inline-block; width: 100%; margin-bottom: 1rem; border-left: 0.375rem solid rgba(255, 102, 0, 1); background-color: rgba(232, 232, 232, 1); font-size: 1.5rem; padding: 0.3125rem 0.625rem }
.wj_title_2 { display: inline-block; width: 100%; font-size: 1.25rem; font-weight: bold; margin-bottom: 1rem }
.wj_title_3 { display: inline-block; width: 100%; font-size: 1rem; font-weight: bold; margin-bottom: 1rem }
.wj_cont { line-height: 180%; margin-bottom: 1rem; font-size: 1rem }
.wj_img { display: inline-block; width: 100%; margin-bottom: 1rem }
.wj_code { margin-top: 0 !important; margin-bottom: 1rem !important; font-size: 0.875rem !important }
.wj_table { border: 1px solid rgba(255, 136, 56, 1); border-collapse: collapse; margin-bottom: 1rem }
.wj_table tr { display: table-row; vertical-align: inherit }
.wj_table tr th { display: table-cell; vertical-align: inherit; font-weight: normal; border: 1px solid rgba(255, 136, 56, 1); padding: 5px 10px; background-color: rgba(255, 102, 0, 1); color: rgba(255, 255, 255, 1); text-align: left }
.wj_table tr td { display: table-cell; vertical-align: inherit; border: 1px solid rgba(255, 136, 56, 1); padding: 0.3125rem 0.625rem; background-color: rgba(255, 255, 255, 1); text-align: left }
.wj_link, .wj_link:link, .wj_link:visited { color: rgba(51, 51, 51, 1); text-decoration: underline }
.wj_link:hover, .wj_link:active { color: rgba(255, 102, 0, 1) }
.wj_watermark, .wj_watermark :link, .wj_watermark :visited, .wj_watermark :hover, .wj_link:active { color: rgba(255, 255, 255, 1) !important; cursor: