What is a Context Diagram and what does it show?
A one-bubble view: the system in the middle, surrounded by every external actor that interacts with it, each connected by a labelled arrow describing the interaction.
A Context Diagram is the simplest model of a system's scope. You draw the system as a single node and place all external actors (people, organizations, or other systems) around it, then label each connection with what that actor does with the system. It deliberately hides all internal detail — its only job is to fix the system boundary and reveal who talks to the system.
Context Diagram Elements:
- Central system (the system being developed)
- External actors/stakeholders surrounding it
- A labelled relationship from each actor to the system
Worked example — a mobile payment app. Imagine you're scoping an app that lets shoppers pay with their phone. The single central node is "Mobile Payment". Three actors surround it:
- Customer — uses the payment (taps to pay).
- Bank — manages and executes the transactions (moves the money).
- Seller — starts a sale (rings up the purchase).
That's the whole diagram. Even from this skeleton you can already see the three parties whose needs you'll have to gather requirements from.
Why start here: the context diagram is the first step in use-case modelling. Naming every actor up front means you won't forget a stakeholder when you elicit requirements — a missing actor late in a project is an expensive surprise.