Context diagram — highest level view of system and its environment.
Elements:
Example:
[Customer] ←→ ┌──────────────┐ ←→ [Payment Gateway]
│ │
[Admin] ←→ │ Order System │ ←→ [Warehouse]
│ │
[Reports] ←→ └──────────────┘ ←→ [Email Service]
Benefits:
BA role: Create context diagram early in project.