16. Data Flow Diagrams (cont)

Multiple level Data Flow Diagrams

Complicated data flow diagrams can be several layers deep.

In the example above Process 1 'Confirm order detail' has its own DFD as well. This shows in detail how that particular process works.

Hiding away the extra detail prevents each DFD becoming too cluttered.

The 'top level' or Level 0 DFD is called the 'context diagram' and it provides an overall view of the system. Sometimes this is all that is required but quite often individual top-level processes need to be analysed as well. This is where multiple level DFD become useful.

In a multiple level DFD you may 'drill down' into a process to see what happens to the data in that particular process. This too can hide details of some sub-processes, so drilling down yet again will show their internal data flows.

There are automated tools available to create the more complicated DFD