[Informatics] Query on Practice exam solution

[Garth, Lucas A]

Hi Joseph – if you provide the exam and the question number (and question text if possible) it will make it easier for us to review.

Repeated records is a 1NF concept.  The main thinking behind 1NF is each field contains one piece of data and it’s accessible by a primary key.

Otherwise you could have: name, address, postcode, state, mobile phone 1, mobile phone 2, mobile phone 3.

If someone only has one mobile phone then this creates a problem with the 2nd and 3rd fields being blank.
If someone has three mobile phone numbers you could try to enter 3 mobile phone numbers into only one mobile phone field as an entry but this would also violate 1NF because it would be very hard to identify a specific mobile phone number using the primary key.

Therefore the only real response would be to create a linking table containing name and mobile phone.

This is one of the examples where splitting into two tables would be required in order to achieve 1NF.

I’d also suggest calculated fields should not even be in a database at 1NF as well, though some people are keen to see them stay.  In general they don’t satisfy “the key” requirement (1NF) let alone “the whole key” (2NF) and “nothing but the key so help me Codd” (3NF).

Lucas
Lalor SC

From: informatics-bounces at edulists.com.au [mailto:informatics-bounces at edulists.com.au] On Behalf Of Joseph Papaleo
Sent: Friday, 28 October 2016 10:48 AM
To: Year 12 VCE Informatics Teachers' Mailing List
Subject: [Informatics] Query on Practice exam solution

Hi all,

I am seeking some clarity please on normalisation.

A practice exam multiple choice question asks students to identify which table has achieved FIRST normal form.  The solutions provided refer to answer D being incorrect as there are repeated records.  Isn’t this 2nd normal form?

Thanks
Joseph








Joseph Papaleo

Member of Staff

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[Ave Maria College]<http://www.avemaria.vic.edu.au>



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