[Year 12 IT Apps] Database relationships

Wed Jul 23 21:14:10 EST 2008

An example of a one-to-one relationship would be something like a 'person'
entity and a 'medicare card' entity - one person can only have one medicare
card, and one medicare card can only belong to one person.

Kind regards

Allan Barnes, CEO

Australian Institute of Education and Training

P.O. Box 171

Brunswick West 3055

Ph: (03) 9387 2051

FAX: (03) 9387 3470

Mobile: 0409 428 221

From: itapps-bounces at edulists.com.au [mailto:itapps-bounces at edulists.com.au]
On Behalf Of Mia Alexiou
Sent: Wednesday, 23 July 2008 9:05 PM
To: Year 12 IT Applications Teachers' Mailing List
Subject: Re: [Year 12 IT Apps] Database relationships

Hi all,

I'm an intruder here (I tech year 11 not year 12) but I thought I could
share my somewhat rusty knowledge of databases.

In response to Lisa's question the employee/department relationship is
one-to-many.   As for "true" one-to-one relationships I've never seen one in
action and so doubt they are common at a small database level.  That being
said, I can think of a couple of situations where they might be useful such
as splitting commonly needed data from that which is rarely needed, to
reduce the time it takes to run queries over a huge table.  Another reason
might be security, with highly sensitive data being stored in a separate
table.

A 0 or 1 to-many relationship is much more common and is what most people
(even in industry) usually mean when they talk about one-to-one
relationships.  These are explained nicely (under the one-to-one heading!)
at http://www.onlamp.com/pub/a/onlamp/2001/03/20/aboutSQL.html.

I hope this was helpful

Mia Alexiou
RMIT TAFE
Information Technology
Sessional Teacher

On Wed, Jul 23, 2008 at 6:10 PM, Lisa Imms <lisimms at copticvic.org> wrote:

Hi Mark,

Firstly, thanks for the resource :-)

I hate to even contemplate disagreeing with you as my ITA class and I regard
you as the ITA font-of-all-knowledge, but I will try this anyway.....

Your example for one-to-one: "E.g. an employee's department data in one
table matches a corresponding department in another table, allowing data
relating to that department to be fetched."

Wouldn't this be a one to many relationship? Even the line you have joining
them has the 'many feathers' at the employees table? Although each employee
can belong to only one department, each department can (and will) have
multiple employees? So it is actually a one to many relationship?

Am I correct in assuming that a well organised database would not have any
one-to-one relationships? The two tables in a one-to-one relationship
could/should just be merged into one table?

Lisa Bairstow
St Mary's Coptic Orthodox College

________________________________

From: itapps-bounces at edulists.com.au on behalf of Mark Kelly
Sent: Wed 7/23/2008 2:24 PM
To: Year 12 IT Applications Teachers' Mailing List
Subject: [Year 12 IT Apps] Database relationships

Hi all.  It's been mighty quiet here for a while.  To perk things up,
here's a little revision for database relationships (1-1, 1-many,
many-many) that may or may not be useful.

Cheers
Mark

--
Mark Kelly
Manager - Information Systems
McKinnon Secondary College
McKinnon Rd McKinnon 3204, Victoria, Australia
Direct line / Voicemail: 8520 9085
School Phone +613 8520 9000
School Fax +613 95789253
kel AT mckinnonsc.vic.edu.au

Webmaster - http://www.mckinnonsc.vic.edu.au
<http://www.mckinnonsc.vic.edu.au/>
IT Lecture notes: http://vceit.com <http://vceit.com/>

Moderator: IT Applications Mailing List

If you Declare War - is it integer or boolean?
_______________________________________________

http://www.edulists.com.au <http://www.edulists.com.au/>  - FAQ, resources,
subscribe, unsubscribe

IT Applications Mailing List kindly supported by
http://www.vcaa.vic.edu.au/vce/studies/infotech/itapplications3-4.html -
Victorian Curriculum and Assessment Authority and

http://www.vitta.org.au <http://www.vitta.org.au/>   - VITTA Victorian
Information Technology Teachers Association Inc

_______________________________________________
http://www.edulists.com.au - FAQ, resources, subscribe, unsubscribe
IT Applications Mailing List kindly supported by
http://www.vcaa.vic.edu.au/vce/studies/infotech/itapplications3-4.html -
Victorian Curriculum and Assessment Authority and
http://www.vitta.org.au  - VITTA Victorian Information Technology Teachers
Association Inc

_______________________________________________ 
http://www.edulists.com.au  <http://www.edulists.com.au> - FAQ, resources,
subscribe, unsubscribe 
IT Applications Mailing List kindly supported by 
http://www.vcaa.vic.edu.au/vce/studies/infotech/infotechindex.html
<http://www.vcaa.vic.edu.au/vce/studies/infotech/itapplications3-4.html%20>
- Victorian Curriculum and Assessment Authority and 
http://www.vitta.org.au  <http://www.vitta.org.au> - VITTA Victorian
Information Technology Teachers Association Inc

  _____  

Message protected by MailGuard: e-mail anti-virus, anti-spam and content
filtering.
http://www.mailguard.com.au/mg

Report
<https://login.mailguard.com.au/report/1vuYjlI9hA/408s2xedFO3BSztpPnlZPi/0.0
04>  this message as spam  

No virus found in this incoming message.
Checked by AVG - http://www.avg.com
Version: 8.0.138 / Virus Database: 270.5.4/1567 - Release Date: 7/22/2008
4:05 PM

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.edulists.com.au/pipermail/itapps/attachments/20080723/2c17dd84/attachment-0001.html