AQA Computer Science A Level

Level 0 to Level 1 DFD
By Admin - May 26, 2020, 2:53 p.m.
Last Edit - June 1, 2020, 1:36 p.m.

So, you have a Level 0 DFD (or syntax diagram) and now need to take it to the next level. Remember your Level 0 DFD only shows the interactions with the system, you now need to look at each interaction to identify a Process and any Data Stores.

I will use this example for the rest of this post:


p.s. I'm not sure what this example means by up/down hotel info. Also Reservation / Cancellation info should really be two arrows.

Converting Level 0 to Level 1

Step 1

Pick one of the arrows on your Level 0 DFD, I will pick Fill reservation form..

Step 2

Add the entity involved to your Level 1 diagram.


Step 3

Create a process, then give it a name. The name is important, and can often be gathered by using the labelling of the line. If it's an input, then you can often add the word Get in front of the label name. If it's an output, then you can often add the word Calculate in front of the label name.


Alternative names could be Make Reservation, or Get Reservation Info. You also need to label the arrow with the items passed into the process.

Step 4

Now you have a process, we need to add the data handling, So if process is to handle an input, then the data inputted should be passed to a Data Store for future use. If there is some sort of checking or other calculation involved, you may need to also retrieve data from a Data Store.


If your process is to handle an output, then you will need to retrieve data from a Data Store in order to produce the output or to perform any calculations needed to produce the output.


The D label on the Data Store is to indicate a Digital store, a Manual store will be labelled M instead. A Manual Data Store would be written documents or files.

Step 5

You have now completed your Level 1 DFD for the first interaction. Remember each line from your Level 0 DFD should only create ONE process. You should now repeat steps 1 to 4 until you have covered every interaction on your Level 0 DFD.

Remember your Level 1 DFD can have the same entity on the diagram multiple times. So to make this diagram easier to create, make sure you do use a new copy of the entity to make better use of space.