[Informatics] Data normalisation

[Pearse, Steven S]

That is why they have barrier techniques in the study design Mark. To stop the chimps!

Good work study design!  +1.


From: informatics-bounces at edulists.com.au [mailto:informatics-bounces at edulists.com.au] On Behalf Of Mark
Sent: Tuesday, 4 October 2016 10:44 PM
To: Year 12 VCE Informatics Teachers' Mailing List <informatics at edulists.com.au>
Subject: Re: [Informatics] Data normalisation

As I've always said: if you create 2NF problems, you should not be in charge of a database.
2NF problems only occur because of stupid design - using multiple existing fields as a key.

It irks me when exams artificially labour 2NF scenarios. It seems like a medical school exam asking students to explain how to treat the infection caused by letting rabid chimpanzees into the operating room during an operation.

The only correct answer is: don't be dumb enough to let the frothy chimps in.

On Tuesday, 4 October 2016, Matheson, Heath A <Matheson.Heath.A at edumail.vic.gov.au<mailto:Matheson.Heath.A at edumail.vic.gov.au>> wrote:
Hi Gang,
I went and had another look at Mark’s normalisation slideshows from his website, definitely not from my computer or Litsa’s e-mail. I still really struggle to explain the practical difference between 2NF and 3NF, I think because I see the purpose of doing 2NF and 3NF to be the same (data integrity).  I have no problems in normalising to third level. I find that easy. But I think if asked to turn 1NF to 2NF I would go straight to 3NF. This would be faster than trying to work out what I can leave to make it 2NF. So I need some help.
From the example slideshow:
[cid:image003.png at 01D21E95.DA30FE50]
But if you said “One reason this table is not 2NF is that House Colour is not dependent on Subject” would you be wrong? What makes you wait until later to deal with House Colour?
Also, If you were asked to make (or describe how to make) a database 2NF and you made it 3NF could you be marked down? I would think not.

Cheers,
Heath Matheson
Mount Soggy Secondary College

From: informatics-bounces at edulists.com.au<javascript:_e(%7B%7D,'cvml','informatics-bounces at edulists.com.au');> [mailto:informatics-bounces at edulists.com.au<javascript:_e(%7B%7D,'cvml','informatics-bounces at edulists.com.au');>] On Behalf Of Mark
Sent: Tuesday, 4 October 2016 8:48 PM
To: Year 12 VCE Informatics Teachers' Mailing List
Subject: Re: [Informatics] Data normalisation

Hi Robert.  Thanks for the message.

I have no worries about criticism of my materials.

The status of message recalls has never come up before, so I thought it timely to establish a policy for the future.

Regards
Mark

On Tuesday, 4 October 2016, Robert Hind <robert at yinnar.com<javascript:_e(%7B%7D,'cvml','robert at yinnar.com');>> wrote:
Sorry Mark.
And sorry that I ended up criticising one of your PowerPoint presentations which is freely available on your own vceit website.

Robert Hind
Ex Traralgon and Ashwood
Retired

________________________________
From: informatics-bounces at edulists.com.au<mailto:informatics-bounces at edulists.com.au> [mailto:informatics-bounces at edulists.com.au] On Behalf Of Mark
Sent: Tuesday, 4 October 2016 7:25 PM
To: Year 12 VCE Informatics Teachers' Mailing List
Subject: Re: [Informatics] Data normalisation
I would have thought that if the sender of a message said that the post was not intended for the list, recipients would delete it, and certainly not respond to its contents.

On Tuesday, 4 October 2016, Robert Hind <robert at yinnar.com<mailto:robert at yinnar.com>> wrote:
Well Litsa you did send the ppt files to all of us and I was interested enough to have a look at the example file.

Now I must take exception to slides 26 and 27 - pics below

Both the statements on yellow background are false. The HouseColor depends only on the HouseName (or vice versa), not directly on the StudentID.

As almost noted in slide 28 " These two non-key fields are more dependent on each other than they are on the primary key"

The key 3NF rule here is: "remove to a new table any non-key attributes that are more dependent on other non-key attributes than the table key"

So we move HouseName and HouseColor to a new table and leave just HouseName in the Student table.

Robert Hind
Ex Traralgon and Ashwood
Retired

[cid:image004.jpg at 01D21E95.DA30FE50]
[cid:image005.jpg at 01D21E95.DA30FE50]

________________________________
From: informatics-bounces at edulists.com.au<javascript:_e(%7B%7D,'cvml','informatics-bounces at edulists.com.au');> [mailto:informatics-bounces at edulists.com.au<javascript:_e(%7B%7D,'cvml','informatics-bounces at edulists.com.au');>] On Behalf Of Litsa Tzelepis
Sent: Tuesday, 4 October 2016 2:54 PM
To: Year 12 VCE Informatics Teachers' Mailing List
Subject: [Informatics] Data normalisation


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