[Year 12 IT Apps] Normal forms

[Mark KELLY]

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, Fax +613 9578 9253
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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