How to Draw a Level 1 Data Flow Diagram in Visio (DFD Step by Step)
A level 1 data flow diagram opens up the single box of a context diagram into its main processes and data stores. Learn how to number processes, add data stores and keep flows balanced, with an online shop in Visio.
Step by step
- DFD level 1. A context diagram shows a system as one box. A level one data flow diagram opens that box up. Let's draw one in Visio for a small online shop.
- Gane-Sarson stencil. I'm using the Gane Sarson stencil. Same four shapes as always.
- External entity. The external entities stay outside, just like on the context diagram. Start with the customer.
- Numbered processes. Now the main processes inside the system. Give each one a number, so the next level down can refer to it. Process one, take order.
- Label every flow. The customer sends the order in. Label the flow with the data, not the action.
- Data stores. At level one, data stores appear for the first time. Orders are kept in store D one. Take order writes the new order to the store.
- Numbered processes. Process two, take payment.
- Label every flow. It needs the order total from process one.
- External entity. The payment provider is outside our system, so it's another external entity.
- Label every flow. Connect it with a payment request.
- Numbered processes. Process three, ship order. It reads paid orders from the store.
- Label every flow. Connect the store to it. Data can flow out of a store into a process.
- External entity. A courier delivers the parcel, and it's outside our system too.
- Label every flow. Shipping sends the courier a dispatch note.
- Done. Click away to see the level one diagram.
- 3 level 1 rules. Three rules. Number every process. Every flow on the context diagram must show up here too, that's called balancing. And data never moves between two stores or two entities without a process.
