@startuml cause-effect
title 因果图 — 登录功能输入验证

' ========== 布局 ==========
left to right direction
skinparam defaultTextAlignment center
skinparam rectangle {
    RoundCorner 15
}

' ========== 原因 (Causes) ==========
rectangle "原因" as causes {
    rectangle "C1\n账号长度 ≥ 6" as C1 #LightBlue
    rectangle "C2\n账号长度 ≤ 10" as C2 #LightBlue
    rectangle "C3\n账号为纯数字\n（自然数）" as C3 #LightBlue
    rectangle "C4\n密码长度 = 8" as C4 #LightBlue
}

' ========== 中间节点 ==========
rectangle "M1\n账号合法\n(C1 ∧ C2 ∧ C3)" as M1 #Wheat

' ========== 结果 (Effects) ==========
rectangle "结果" as effects {
    rectangle "E1\n显示\"输入合法\"" as E1 #LightGreen
    rectangle "E2\n显示\"账号不合法\"" as E2 #Salmon
    rectangle "E3\n显示\"密码不合法\"" as E3 #Salmon
}

' ========== 关系 ==========
C1 --> M1 : AND
C2 --> M1 : AND
C3 --> M1 : AND

M1 --> E1 : AND
C4 --> E1 : AND

M1 ..> E2 : NOT\n(~M1 → E2)
C4 ..> E3 : NOT\n(~C4 → E3)

' ========== 约束 ==========
note bottom of causes
  约束: C1, C2, C3 相互独立
  C4 独立于 C1/C2/C3
end note

@enduml