用例图-包含关系

+-------------------+
|    用户           |
|    (Actor)        |
+-------------------+
         |
         |
         v
+-------------------+
|  浏览商品         |
|  (Use Case)       |
+-------------------+
         |
         |
         v
+-------------------+        +-------------------+
|  添加商品到购物车 |        |  用户登录         |
|  (Use Case)       |<-------|  (Use Case)       |
+-------------------+        +-------------------+
         |
         |
         v
+-------------------+
|  结账             |
|  (Use Case)       |
+-------------------+
         |
         |
         v
+-------------------+
|  用户登录         |
|  (Use Case)       |
+-------------------+

@startuml
actor 用户 as User

usecase 浏览商品 as BrowseProducts
usecase 添加商品到购物车 as AddToCart
usecase 结账 as Checkout
usecase 用户登录 as UserLogin

User --> BrowseProducts
User --> AddToCart
User --> Checkout

Checkout --> UserLogin : <<include>>
AddToCart --> UserLogin : <<include>>
@enduml