How to Draw a Context Diagram in Visio (DFD Level 0)
A context diagram is the one-page picture of a system and everything it talks to. Learn how to draw a level 0 data flow diagram in Visio for an online shop, step by step.
Step by step
Intro
- Context diagram. A context diagram is a one-page picture of a system's scope. It has one box for the system in the middle, and every outside person, team or system that swaps data with it around the edge.
- Gane-Sarson stencil. Use the Gane-Sarson stencil in the Shapes pane. A context diagram is a data flow diagram with only one process, so you only need the Process shape, the Interface shape and the Data Flow connector.
The system
- The system. Drag a Process shape to the middle of the page and type Online Shop System. The whole system is one process. Don't split it into smaller processes. Keeping it as one box is the point of level 0.
Entities and data flows
- External entities. Next, add everything outside the system that sends or receives data. Drag an Interface shape onto the page and type Customer.
- Data flows. Connect Customer to Online Shop System with a Data Flow connector and label it Order. The arrow points at the system because the customer sends the order in.
- External entities. Add a second Interface shape called Payment Provider. The system asks it to take the money.
- Data flows. Draw a Data Flow from the system to Payment Provider and label it Payment request.
- External entities. Add a third one called Warehouse, which needs to know what to pack.
- Data flows. Draw a Data Flow from the system to Warehouse labelled Pick list.
- External entities. Add a fourth one called Accounts Team, which gets a daily sales report.
- Data flows. Draw a Data Flow from the system to Accounts Team labelled Sales report.
- Done. Click an empty part of the page to deselect everything. The whole scope now fits on one page: 1 process, 4 external entities and 4 labelled data flows.
Why BAs love it
- Why BAs love it. Show the diagram to stakeholders early. If someone asks "what about the courier?", you have found a missing interface before anyone writes code. Add it as another Interface shape with its own labelled data flow.
Common mistakes
- Splitting the system into several processes. A context diagram has exactly one process. Smaller processes like Take payment or Pack order belong in the next diagram down (level 1).
- Adding data stores to the context diagram. Databases inside the system are hidden at this level. Only show the system, the external entities and the data flows between them.
- Arrows with no label, or a vague one. Every Data Flow needs a label that names the data, like Order or Pick list. An arrow labelled "data", or with no label at all, gives stakeholders nothing to check.
- Joining two external entities to each other. A flow from Customer to Warehouse happens outside your system, so it is out of scope. Only draw flows that go into or out of the one process.
When a business analyst uses this
Before a scoping workshop, draw the context diagram and walk stakeholders through each arrow. Every external entity becomes an interface to list in the requirements. Anything missing, like a courier, goes in the RAID log or the scope list before sign-off.
Questions people ask
How do I make a context diagram in Visio?
Open the Gane-Sarson stencil and drop 1 Process shape for the whole system. Add an Interface shape for each outside party, then join each one to the system with a labelled Data Flow connector.
How do I draw a data flow diagram in Visio?
Use the same Gane-Sarson stencil. The context diagram is the top level with 1 process. For a more detailed data flow diagram, break that process into smaller processes and add data stores where data is kept.
How do you draw a context diagram?
Put the system in the middle as one box. Add every person, team or system that sends it data or gets data from it, then draw a labelled arrow for each flow. The rules are the same in any diagram tool.
