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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">For normalisation I talk about three problems you can have with databases and why they are problems.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Too many “things” in one field, which makes it hard to search and sort.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Data repeated in many rows which means if something changes such as a customer address you need to change it in lots of places.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Tables that contain calculated values which take up processing power and unnecessary storage space if you have a really, really large database.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:18.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:18.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">0NF – has all the problems<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:18.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">1NF – eliminate problem 1 (separate the data)<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:18.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">2NF – eliminate problem 1 and 2 (make multiple tables, add primary keys and link them)<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:18.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">3NF – eliminate all three problems. (eliminate calculated fields, put them in queries and reports)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I think that’s all they need to know based on the VCAA examination reports so far.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Good luck to all your students!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Heath Matheson<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Mount Beauty Secondary College<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> itapps-bounces@edulists.com.au [mailto:itapps-bounces@edulists.com.au]
<b>On Behalf Of </b>ken price<br>
<b>Sent:</b> Wednesday, 5 November 2014 10:40 AM<br>
<b>To:</b> Year 12 IT Applications Teachers' Mailing List<br>
<b>Subject:</b> Re: [Year 12 IT Apps] Third Normal Form<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">It's not often that I'd consider normalisation as a source of interesting reading, but this is rather good. Well done Mark - hopefully this will help others, or at least provide a direct example they can use. <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Is it OK for it to be re-used elsewhere with acknowledgement?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Ken Price<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Nov 5, 2014 at 10:20 AM, Mark <<a href="mailto:mark@vceit.com" target="_blank">mark@vceit.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hello workers.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In case anyone was waiting for the other shoe to drop, let's cover 3NF.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">To achieve 3NF:<o:p></o:p></p>
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<p class="MsoNormal">- You must have already achieved 1NF and 2NF.<o:p></o:p></p>
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<p class="MsoNormal">- No non-key field may be dependent on another non-key field.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Another way of saying it is that every non-key field in a table must give some information about the primary key rather than any other key in the table. Any field that does not contribute to the description of the primary key must be removed
from the table.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">For example... take a table. StudentID+SubjectID together are the primary key. (BTW - this use of multi-field keys is always to be avoided in the real world, but never mind for now.)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Honours is a Boolean field that is True if Mark is A or above, and False otherwise.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">StudentID SubjectID Mark Honours</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">ABC0001 S01 A True </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">ABC0001 S02 A+ True</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">DEF0002 S01 B False</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">The Honours field is dependent on the Mark field (i.e. to find the meaning of the Honours field, you need to refer to the Mark field) - but the Mark field is not the table's primary key. i.e.
The Honours field describes the mark, not the student+subject.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">So, a non-key field (Honours) is dependent on another non-key field (Mark). So it fails 3NF.</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">To fix it, do the same as we did before to achieve 2NF... break the offending field away into its own table with its own primary key (Mark) and non-key field (Honours) and relate the new table
to the existing one using Mark as the link field.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">This 3NF scenario looks VERY much like the 2NF before, doesn't it? </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">The only difference is that 2NF needed a non-key field to relate to the entire set of fields acting as the primary key.</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">In 3NF, it's actually simpler - a non-key field must not be dependent on another non-key field. In both cases, the fix is the same: table splitting. </span>In my opinion, 3NF should be called
1.5NF because it seems to be more basic that 2NF, but we must all revere the word of Codd.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">Always remember the normalisation oath:</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">The key (1NF), the whole key (2NF) and nothing but the key (3NF), so help me
</span><a href="http://en.wikipedia.org/wiki/Edgar_F._Codd" target="_blank"><span style="font-family:"Arial","sans-serif"">Codd</span></a><span style="font-family:"Arial","sans-serif"">.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">(It's taken me 4 years, but I think I'm <i>finally</i> getting the hang of normalisation).<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#888888"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="hoenzb"><span style="color:#888888">-- </span><o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="color:#888888">Mark Kelly<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888">mark AT vceit DOT com<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888"><a href="http://vceit.com" target="_blank">http://vceit.com</a><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888"><o:p> </o:p></span></p>
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<p class="MsoNormal"><i><span style="color:#888888">I love the sound of people's voices after they stop talking.</span></i><span style="color:#888888"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888"><o:p> </o:p></span></p>
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<p class="MsoNormal"><br>
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<p class="MsoNormal"><br>
<br clear="all">
<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
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<p class="MsoNormal">-- <br>
Dr Ken Price MACS CP ACCE Professional Associate.<br>
President, TASITE <a href="http://www.tasite.tas.edu.au" target="_blank">http://www.tasite.tas.edu.au</a><o:p></o:p></p>
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