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Level 2 DFDs

We now create the Level 2 Data Flow Diagrams. A possible solution is as shown below. We describe each function using two to seven sentences. These sentences then become the function's processes. Since this is a simple system, we will use two processes for each function:

Function 1 - Process Order

  1. Receive order
  2. Issue invoice and goods.

Function 2 - Process Payments

1. Receive payment
2. Issue receipt and catalogue

Let us show this diagrammatically. First 'expand' the function boxes so that we can fit the process boxes into them. Then position the data flows from Level 1 into the correct process in Level 2.

Level 2 DFD

Now apply the 'three rules':

  1. Q Does every process have inputs and outputs?

A No. Process 1.2 has no inputs. We will deal with this shortly.

  1. Q Does each process have all the information it needs to produce its output?

A No. Process 1.1 does, Process 1.2 does not.

  1. Q What information does Process 1.2 need and where will it get this from?

A It needs order details and it will get these from Process 1.1.

Next: Updated Diagram