[Year 12 SofDev] A DFD theory challenge!

[Allan Barnes]

Me again. Sorry.

 

A data store is where data is stored (sounds silly doesn't it?).

 

A data store is therefore worthless if data is not written to it and taken
from it, but it can still exist as a data store. There just is no point to
it and it would be considered poor design. Consider - if no 'new' or ongoing
data is written to a data store then you can only take limited information
out of it as no new information will be sent to it. If you don't take
information out of it then what is the point of saving information to it?
In this example, you can't take customer orders from the data store if the
waiter does not save the orders to the system. So the data store needs data
to be saved to it in order for the chef to retrieve it.

 

If it is written to system 1 and then read from system 2, the information
would therefore need to be sent from 1 to 2 (begging the question why?). 

 

I would have thought that as the text file holds data it therefore needs to
be displayed as a data store in the DFD. Or two. At level 1 DFD I think you
can only show 1 system by definition (?), if you go to a Level 2 DFD which I
don't think is required at Year 12 level, you would show the 2 systems.

 

 

 

 

Kind regards

 

Allan Barnes, CEO

Australian Institute of Education and Training

P.O. Box 171

Brunswick West 3055

Melbourne, Victoria

Ph: (03) 9387 2051

FAX: (03) 9387 3470

Mobile: 0409 428 221

 

 

 

 

From: sofdev-bounces at edulists.com.au [mailto:sofdev-bounces at edulists.com.au]
On Behalf Of Mark KELLY
Sent: Friday, 29 July 2011 9:37 AM
To: Year 12 Software Development Teachers' Mailing List
Subject: [Year 12 SofDev] A DFD theory challenge!

 

Hi all. As I ponder the Mexican Cantina detailed example of SD U4O1 in the
study design, I find the DFD increasingly interesting.

The case study says that the student's mobile software (call it system 1)
writes an order to a text file.
The other software (call it system 2) reads the text file and transmits it
to the kitchen.

The question is: Is the text file a 'data store'?  What constitutes a data
store?  
Does it need to be both written to and read to qualify as a data store?
Does it need to be written/read by the same system?
Or can it be read/written by 2 systems?
If it's only written by system1, and then left somewhere to be read by
system 2, does it still count as part of system 1?

Therefore: Should the text file be shown as a data store in the DFD?
Should system 2 be shown as an external entity getting input from the text
file?
Will Saint Kilda get into the final 8 this season?

Draft DFD attached.
-- 
Mark Kelly
Manager of ICT, Reporting, IT Learning Area
McKinnon Secondary College
McKinnon Rd McKinnon 3204, Victoria, Australia
Direct line / Voicemail: +613 8520 9085, Fax +613 9578 9253
kel at mckinnonsc.vic.edu.au
VCE IT Lecture Notes: http://vceit.com
Moderator: IT <http://www.edulists.com.au/>  Applications Edulist

Want a good time? Call 0112358. Ask for Mr Fibonacci.

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