[Year 12 IT Apps] Normal forms

[Mark Scott]

Joseph

Your explanation looks and sounds simple enough but...

There are at least half a dozen different definitions of this process. (although the 1NF explanation is fairly consistent)

And, most importantly, we still do not know how the VCAA (Hi Paula) defines the process of Normalisation and in particular the first three forms.

I'm expecting a very simple question on this on the exam (hopefully just a 1NF question).

Anything too complicated and this mailing list will be on fire after the exam.

thanks
Mark Scott
Luther College

"Don't water the rocks" Gerry Smith, River Oaks Public School

From: itapps-bounces at edulists.com.au [mailto:itapps-bounces at edulists.com.au] On Behalf Of Joseph Papaleo
Sent: Monday, 17 October 2011 1:36 PM
To: Year 12 IT Applications Teachers' Mailing List
Subject: Re: [Year 12 IT Apps] Normal forms

Mark,
In a nutshell, I've taught it as :

1NF - tidy the table(s) up horizontally
ie Fields contain only a single value eg Name: Mr Barney Rubble changes to
Title: Mr
Fname: Barney
Sname: Rubble

Remove repeating Groups (as per Mark's comments)


2NF - Tidy the table(s) up Vertically
Eliminate duplication in records down the table by using a Primary Key that each record refers to.
Continue to do this as often as required until duplication is removed from all tables- students should see the need for a new table if there is duplication with their own unique Primary Key.


3NF - Make all fields in a table Mutually Exclusive
ie, no field can rely on another.  eg table may contain "Quantity" and "Price", but it cannot contain "Total Cost" as Total cost = Quantity x Price.

I'm concerned that my students understand this, but they found it difficult to do. Also concerned that I may have used an old or inferior resource.




Joseph Papaleo
Ivanhoe Grammar School,
Plenty Campus



On Mon, Oct 17, 2011 at 1:04 PM, Mark KELLY <kel at mckinnonsc.vic.edu.au<mailto:kel at mckinnonsc.vic.edu.au>> wrote:
Groan.  I just spent another 30 minutes trying to explain the differences between 2NF and 3NF to my dears.
As usual, by the time I finished, I think they knew less than when I started.

1NF is pretty clear cut...
  - no duplicate rows (i.e. identical records)
  - no multiple columns that contain the same *type* of data (e.g. child1, child2, child3)
  - only one piece of data per field (e.g. don't store 2 phone numbers for a person in the 'phone' field; put street address/suburb/postcode in separate fields; in Filemaker, don't use repeating fields)

But 2NF is really only a problem if you use *multiple* fields as a key (e.g. using firstname + lastname + phone as a unique key) instead of using a unique and arbitrary key field, like an ID number.
I realise now that my kids have trouble absorbing 2NF because at no time in their database education have I ever *mentioned* the possibility of using multiple fields as the key. So explaining 2NF to them was a bit like warning them not to walk using their ears - the concept had never even dawned on them before. To them, having a non-key field that did not give information about *all* of the key fields was a strange and scary possibility.

3NF is, I think, relatively straight forward. Each non-key field must give information about the key and not to another non-key field.  Violation of 3NF is usually pretty obvious because it looks "strange".

After 2 slideshows, I'm still trying to work out a way to make it sound really clear...  next time, maybe. If anyone has hit on a sure-fire summary of differentiating normal forms, I'd love to hear of it.

Regards

--
Mark Kelly
Manager of ICT, Reporting, IT Learning Area
McKinnon Secondary College
McKinnon Rd McKinnon 3204, Victoria, Australia
Direct line / Voicemail: +613 8520 9085<tel:%2B613%208520%209085>, Fax +613 9578 9253<tel:%2B613%209578%209253>
kel at mckinnonsc.vic.edu.au<mailto:kel at mckinnonsc.vic.edu.au>
VCE IT Lecture Notes: http://vceit.com
Moderator: IT Applications Edulist<http://www.edulists.com.au/>

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

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