Mark,<br>In a nutshell, I've taught it as :<br><br>1NF - tidy the table(s) up horizontally<br>ie Fields contain only a single value eg Name: Mr Barney Rubble changes to <br>Title: Mr<br>Fname: Barney <br>Sname: Rubble<br clear="all">
<br>Remove repeating Groups (as per Mark's comments)<br><br><br>2NF - Tidy the table(s) up Vertically<br>Eliminate duplication in records down the table by using a Primary Key that each record refers to.<br>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.<br>
<br><br>3NF - Make all fields in a table Mutually Exclusive<br>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.<br>
<br>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.<br><br><br><br><br>Joseph Papaleo<br>Ivanhoe Grammar School,<br>Plenty Campus<br>
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<br><br><div class="gmail_quote">On Mon, Oct 17, 2011 at 1:04 PM, Mark KELLY <span dir="ltr"><<a href="mailto:kel@mckinnonsc.vic.edu.au">kel@mckinnonsc.vic.edu.au</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
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><font color="#888888"><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: <a href="tel:%2B613%208520%209085" value="+61385209085" target="_blank">+613 8520 9085</a>, Fax <a href="tel:%2B613%209578%209253" value="+61395789253" target="_blank">+613 9578 9253</a><br>
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