DataFlow Modelling

DataFlow Modelling is a very old technique, at least in the computing world.  It seems to have fallen out of favour, replaced by more trendy state models or object models.  This is a shame as data flow diagrams are so simple and intutitive that they can be used without explanation, even with people that have not encountered them before.  Try that with a State model or an object model…….

One reason that data flow diagrams are not used so often is that the tools to draw them do not seem to be available readily.  To remedy this I have written a simple DataFlowModeller in Java for all to use.  It requires Java 8 to run.

Some notes here on how to use the tool.  Let us start to define a calculator:

The first task is to create a ‘Context Diagram’. This defines the way the calculator will interact with its environment. The large circle in the middle represents the program.

  • ‘Long press’ on the large circle and when the dialogue pops up choose the name ‘Caculator’.
  • Right click on the empty space and choose ‘New External’, select a name for it (e.g. User)and press ‘ok’. The user of the program is now represented in the design.
  • Click on the user to select it.  See that an arrow appears on the right hand side.  Drag the arrow to the ‘Calculator’ circle until the arrow and the circle glow green. Drop the arrow.
  • Name the data flow ‘Sums’.  You now show the user presenting sums to the calculator.
  • Now create a new external called ‘Screen’
  • Create a flow from the calculator to the screen, and call it results.

If you want to make a flow into a pleasing curve, then select it and drag part of the line.  This will create a ‘way-point’ in the flow that affects the curve of the line.  You can have as may way-points as you like in a flow.  You can remove a way-point by making it unnecessary. Do this by moving it to a position where it is on a straight line between the points either side. It will then disappear .

When you have designed the way that your calculator will interact with the world you can drill down to the detail of what goes on inside it.  To do this double click on the circle.  You will initially see a screen with a collection of arrows.  (These arrow may be sitting on top of each other, so you may need to drag them to different locations).  The arrows are the flows entering and leaving ‘Calculator’.

You can leave this view and go back to the context diagram either by double-clicking the empty background, or by pressing the up arrow in the menu bar.

In the exploded view you can add transforms (things that act on and change data) and data stores (places that the data rests, like files and databases).  You can connect these with flows to the entering and leaving flows.

Any transform you add can be ‘opened’ by double clicking and fleshed out in detail……


Leave a Reply

Your email address will not be published. Required fields are marked *