Groan. I just spent another 30 minutes trying to explain the differences between 2NF and 3NF to my dears. <br>As usual, by the time I finished, I think they knew less than when I started.<br><br>1NF is pretty clear cut...<br>
- no duplicate rows (i.e. identical records)<br> - no multiple columns that contain the same *type* of data (e.g. child1, child2, child3)<br> - 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) <br>
<br>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. <br>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.<br>
<br>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".<br>
<br>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.<br>
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Regards<br><br>-- <br>Mark Kelly<br>Manager of ICT, Reporting, IT Learning Area<br>McKinnon Secondary College<br>McKinnon Rd McKinnon 3204, Victoria, Australia<br>Direct line / Voicemail: +613 8520 9085, Fax +613 9578 9253<br>
<a href="mailto:kel@mckinnonsc.vic.edu.au" target="_blank">kel@mckinnonsc.vic.edu.au</a><br>VCE IT Lecture Notes: <a href="http://vceit.com" target="_blank">http://vceit.com</a><br>Moderator: <a href="http://www.edulists.com.au/" target="_blank">IT Applications Edulist</a><br>
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