Competition - post a photo you've taken of nature >>

Data Flow Diagrams

Ok, so on level1 you identify say 3 process's, where do you from then?

is level 2 like 3 different diagrams for each different process?

Help, or URL help explaining :biggrin:

Reply 1

erk

Hellllppppp :frown:

Rep available, from tommorw :tongue:

Reply 2

erk

I just spoke to an ICT teacher who said it's better to do it in one diagram, using entitys more than once by putting a a diagonal line in the corner of the circle symbol. So, i'm torn.

Reply 3

guest1984

To do a DFD(data flow diagram), you need to start with a context diagram, identifying the external entity and add date flow to a external entity to another external entity. Then you expand the context diagram into a level one diagram, using the child diagram option.

The level diagram contains processes and data store, and is just an expansion of your context diagram

hope that helps

:smile:

Reply 4

erk

Cheers, but level two is further than level one :smile:

Reply 5

Camford

erk

Cheers, but level two is further than level one :smile:

Only if I have got my DFDs with me... You do a very basic DFD for level 0 with just one process (the system) that links all the external entities. Then you break up this "one process" into smaller chunks for level 1 DFD. But, you don't put storages on level 1. You break the processes in level 1 down even further in level 2 DFD, this time include storage file such as your tables and reports. The key is that one level 2 DFD only discribes one Level 1 process. That's what my computing teacher told the class anyway. Only if I have my DFDs with me... Use visio to do them if you have visio.

Reply 6

erk

Thanks Camford!

My level one has 4 processes, so would you advise me to do 4, level 2 diagrams? or 1, level 2?

Reply 7

Camford

erk

Thanks Camford!

My level one has 4 processes, so would you advise me to do 4, level 2 diagrams? or 1, level 2?

The moral is that you put as much as possible on one A4 sheet of paper. I only managed to put one level 1 process on one sheet, so I had to do 4 separate level 2 DFDs. I remember one of my friends did some (a lot actually) tiny (and somewhat confusing and discontinuous) level 2 DFDs (3 or 4 arrows for data flow and a few data store, looks ugly) for his coursework. You should avoid what he did. It sounds about right that one level 1 process should average one sheet of a4. Remember, one process for one DFD not many little ones. (Not that little ones would be wrong, I just personally think that big ones are cool and more importantly, much much much more impressive than lots of little ones)

Reply 8

erk

Yep, mine was too big and messy so i had to do seperate ones, they took up atleast 2/3s of a side.

Thanks fella :biggrin:

Reply 9

dazmanultra

Have a look through this www.eek2.com/unit5.zip , just some work i did a couple of years ago now, it may help.

Reply 10

MrJ

if you are doing the OCR pre-release then unless the tasks and mark scheme have changed since previous years then you do not need to do a level 2 diagram.

You need to get the marks:

1) an attempt at a context diagram which is a high level diagram showing a box with "RUN SYSTEM" in it, all the external bodies / entities round the edge and the flows into and out of the system. e.g. From cutomer entitiy you may have order going into the system and from the system you may have an invoice.

You get marks for an attempt in the pre-release then in the exam you will have to highlight certain flows - this varies each year and in Jan / Jun exams.

2) Low levele diagrams expect you to break up what is going inot the system and show how the data will be processed and stored.

To get marks for the pre-release you need an attept and at least 3 different processes. In the exam you will be asked for a speciific process if its not in your pre-release then you will be able to draw it on the exam script.

hope this helps

regrads Mr J