What is a Context Model in Use Case analysis?

A Context Model is Step 1: draw the whole system as one box and every actor that touches it — answering "who interacts with this system at all?" before you decompose anything.

Why start here? Before breaking the system into detailed use cases, you need to answer: Who interacts with this system at all? The Context Model forces you to identify every external actor (users, devices, external systems) before diving into details. Missing an actor means missing an entire interface — and every interface is an attack surface.

Structure:

• System = one large oval labeled "System"
• All external actors shown around it
• Lines show which actors interact with the system

If an actor has many functions:

1. Many arrows — one per function (more explicit), OR
2. One arrow — functions listed in notes (cleaner diagram)

Security relevance: Each actor-system connection is a trust boundary. The Context Model is your first map of the system's attack surface.