Development Data Flow Diagrams

Im having real trouble with my data flow diagrams for my A2 computing coursework. I was wondering whether anybody could gimme a crash course in them? I have searched google for a good one to no avail!!

Thanks! Bogomip

 

What do you want to know?

 

How to do them if you will Basically, the basics! The book i have explains them worse than a computer scientist explains linux to a noobie

Ta!

 

A DFD shows how the data moves through the system and what data stores are used. it does not specify what typr of data storage is used or how the data is stored.

Diagram stuff used

Discription of shape: Name of diagram stuff - what it does

A square box : External entity- data source or destination for example a customer order or information such as an invoice.

Rounded rectangle, tall ways up : Process - an operation performed on the data. The recangle, has a small bit devided at top and bottom(this is optional) the top labels the process middle gives brief expanation the bottom says where it takes place. the first word must be an active verb eg validate data, adjust stock level

Code:

   _________
  /          \   
  ------------
 |           |
 |           |
 |           |
 |           |
  ------------
  \_________/

Rectangle on side open on right, with left having side as small box: Data Store - such as a file held on disk or a brank of documents eg. Customers, bookings

Code:

  ________________
 |    |
 |___ |___________

A single sided arrow : Data Flow - The arrow represtents the movement between the above the arrow is labled to show what data is involved

Code:

   _________
  /          \   
  ------------                         ________________
 |           |    Name etc     |    |              
 | make      |----------------->|    |Customers
 | booking   |<---------------  |____|___________
 |           |
  ------------
  \_________/

hope that helped
'doc

 

Is that DFDs as in Gayn and Sarson? I remember a black covered book with linotype printing which I found incredibly simple to read. But that was over 15 years ago.... they still teaching that?

Stu

 

Also if the dataflow is bidirectional, you must have an action and reaction.

 

http://www.data-flow-diagrams.com/index.htm

Chris

 

Note that that site uses circles as process' were that is correct for A2 its common to use the rounded boxes.

'doc

 

DFD's are a generic tool. While there are variations on notation, they are largely interchangeable.

As for what is most common, it really depends on what framework you are working within. For example, Yourdon Structured Method use circles for processes, whereas SSADM uses rectangles...

There is no standard notation, but each variation tends to have the same components & rules...

 

Their was a comma missing from my post so it made it read a bit wrong

notice the comma after correct, in A2 we normally use the rectangles

'doc

 

No, we have a book now with some art on the front, big thick thing with "A2 COMPUTING" Printed on the front

Murdoc, thanks sooo soo much for that, its very useful, thanks for the time

cjmwork2 - That websites good! Im surtprised i couldnt find it on google! maybe its loosing its touch :'(

Thanks for the rest of your replys

 

Im also doing my A Level Computing found this thread pretty usefull.

Thank You everyone.

 

No problem is the book you have got by Heathcote? is so check page 177

i just been finishing my database, had no coding now i have loads.

'doc

 

im doing my degree in software development so i know a fair bit about data flow diagrams, at first they can seem daunting but the more you do them the easier they become, or they have for me,

i used the site that chris mentioned also when learning, along with a few books and course work examples