@startuml
title User Management System
skinparam class {
    BackgroundColor<<class diagram>> Cornsilk
    ArrowColor Black
    BorderColor Black
}

class User {
    - id: int
    - username: string
    - password: string
    - email: string
    - created_at: datetime
    - updated_at: datetime
}

class Role {
    - id: int
    - name: string
    - description: string
    - created_at: datetime
    - updated_at: datetime
}

class Permission {
    - id: int
    - name: string
    - description: string
    - created_at: datetime
    - updated_at: datetime
}

class UserRole {
    - user_id: int
    - role_id: int
}

class RolePermission {
    - role_id: int
    - permission_id: int
}

User -- UserRole
Role -- UserRole
Role -- RolePermission
Permission -- RolePermission
@enduml